Test Device Performance - Middle School Physical Science

1. What is the meaning of $\Delta T$ in $Q=mc\Delta T$?

   $\Delta T=T_{\text{final}}-T_{\text{initial}}$. Delta T represents the change in temperature from start to finish.

2. Identify the better device by efficiency: A is $30\%$ efficient, B is $45\%$ efficient.

   Device B. Higher efficiency means less energy wasted.

3. Calculate electrical energy input for $P=200\,\text{W}$ operating for $t=180\,\text{s}$.

   $3.6\times 10^4\,\text{J}$. $E = 200\,\text{W} \times 180\,\text{s} = 36000\,\text{J} = 3.6 \times 10^4\,\text{J}$

4. Identify the best graph type to compare temperature change over time during a device test.

   Line graph of temperature vs. time. Shows heating patterns and rates visually over time.

5. Identify the correct unit for power $P$ in $P=\frac{E}{t}$.

   Watts (W), where $1\ \text{W}=1\ \text{J/s}$. Power is energy per second, measured in watts.

6. What is the independent variable when comparing devices by changing only the heater type?

   The device or heater type. The heater type is what we deliberately change in the experiment.

7. Identify the correct formula for temperature change when initial and final temperatures are known.

   $\Delta T = T_{\text{final}} - T_{\text{initial}}$. Temperature change is final minus initial temperature.

8. Which option is the best way to improve reliability when testing a thermal device performance?

   Repeat trials and average results. Multiple trials reduce random errors and increase data reliability.

9. What is the main purpose of repeating trials when testing a thermal energy device?

   To improve reliability by reducing random error. Multiple trials average out measurement uncertainties.

10. Calculate thermal energy gained: $m=0.50\ \text{kg}$, $c=4200\ \text{J/(kg}\cdot^\circ\text{C)}$, $\Delta T=2^\circ\text{C}$.

    $Q=4200\ \text{J}$. Use $Q = 0.50 \times 4200 \times 2 = 4200$ J.

11. Identify the correct unit for thermal energy $Q$ in the equation $Q = mc\Delta T$.

    Joules (J). SI unit for energy; kilojoules (kJ) also acceptable for larger values.

12. What is the definition of thermal efficiency for a thermal energy device?

    Efficiency $= \frac{\text{useful energy out}}{\text{total energy in}} \times 100\%$. Ratio of useful output to total input, expressed as percentage.

13. Calculate $q$ for $m=0.50\,\text{kg}$, c=4200\,\text{J/(kg\cdot ^\circ C)}, $\Delta T=10\,^\circ\text{C}$.

    $2.1\times 10^4\,\text{J}$. $q = 0.50 \times 4200 \times 10 = 21000\,\text{J} = 2.1 \times 10^4\,\text{J}$

14. State the formula for heat energy absorbed or released by a substance.

    $Q = mc\Delta T$. Heat equals mass times specific heat times temperature change.

15. Calculate $\Delta T$ if water warms from $18^\circ\text{C}$ to $43^\circ\text{C}$ in a test.

    $25^\circ\text{C}$. $\Delta T = T_{final} - T_{initial} = 43 - 18 = 25$.

16. Calculate $\Delta T$ if $T_i = 20\,^{\circ}\text{C}$ and $T_f = 65\,^{\circ}\text{C}$.

    $45\,^{\circ}\text{C}$. $65°C - 20°C = 45°C$ temperature increase.

17. Calculate electrical energy input when $V = 12\ \text{V}$, $I = 2\ \text{A}$, and $t = 30\ \text{s}$.

    $720\ \text{J}$. $E = 12 \times 2 \times 30 = 720\ \text{J}$

18. Which option best describes a measurable criterion for a thermal device: temperature rise, color, or brand name?

    Temperature rise. Temperature rise is quantifiable; color and brand are not measurable criteria.

19. What is the controlled variable in a fair test of two thermal devices heating water?

    The variable kept the same for both devices. Fair tests require identical conditions except for the tested variable.

20. State the formula to compute electrical energy input to a thermal device.

    $E = Pt$. Energy equals power multiplied by time.

21. Calculate power if a device transfers $E = 6000\,\text{J}$ in $t = 200\,\text{s}$.

    $30\,\text{W}$. $P = \frac{6000}{200} = 30$ watts.

22. What is the dependent variable when testing how heater power affects water temperature change?

    Temperature change $\Delta T$ (or final temperature). Temperature change is what we measure as the outcome.

23. State the formula for power using energy and time.

    $P = \frac{E}{t}$. Power equals energy divided by time (watts = joules/second).

24. What is the best instrument to measure the time needed for a device to heat water?

    Stopwatch or timer. Accurately measures elapsed time for heating duration.

25. Which measurable quantities are required to compute $Q$ for heating water using $Q = mc\Delta T$?

    Mass $m$, specific heat $c$, and temperature change $\Delta T$. These three quantities determine the thermal energy absorbed by water.

26. Calculate $\Delta T$ if $T_{\text{initial}} = 20\,^{\circ}\text{C}$ and $T_{\text{final}} = 65\,^{\circ}\text{C}$.

    $45\,^{\circ}\text{C}$. $\Delta T = 65 - 20 = 45\,^{\circ}\text{C}$ using the temperature difference formula.

27. Compute power if a device transfers $3000\,\text{J}$ in $50\,\text{s}$.

    $60\,\text{W}$. $P = \frac{3000\,\text{J}}{50\,\text{s}} = 60\,\text{W}$

28. Calculate $Q$ for $m = 0.20\,\text{kg}$ of water, $c = 4200\,\frac{\text{J}}{\text{kg}\cdot^{\circ}\text{C}}$, and $\Delta T = 10\,^{\circ}\text{C}$.

    $8400\,\text{J}$. $Q = 0.20 \times 4200 \times 10 = 8400\,\text{J}$ using the heat formula.

29. What does $\Delta T$ mean in the equation $Q = mc\Delta T$?

    $\Delta T = T_{\text{final}} - T_{\text{initial}}$. Temperature change is the difference between final and initial temperatures.

30. State the formula for thermal energy gained or lost by a substance.

    $Q = mc\Delta T$. Relates heat to mass, specific heat capacity, and temperature change.

31. What is the dependent variable when testing a heater by measuring water temperature change?

    Temperature change of the water. The variable you measure (temperature change) as the result.

32. Identify the better heater if Device A gives $\Delta T=12^\circ\text{C}$ and Device B gives $\Delta T=9^\circ\text{C}$ in the same time.

    Device A. Larger temperature change means better heating performance.

33. Calculate $Q$ for $m=200\,\text{g}$, $c=4.18\,\text{J}\,\text{g}^{-1}\,^{\circ}\text{C}^{-1}$, $\Delta T=5^{\circ}\text{C}$.

    $Q=4180\,\text{J}$. $Q = 200 \times 4.18 \times 5 = 4180\,\text{J}$ using the formula.

34. Which option best describes a measurable criterion for testing a thermal energy device?

    A quantity with units, such as power in $\text{W}$ or efficiency in $\%$. Measurable criteria must have numerical values and units for quantitative testing.

35. Which measurable quantities are required to compute $q$ using $q = mc\Delta T$?

    Mass $m$, specific heat $c$, and temperature change $\Delta T$. All three variables in the thermal energy formula must be measured.

36. Identify the dependent variable when testing a cooker by measuring water temperature rise over time.

    Water temperature change (or heating rate). The measured outcome that depends on the cooker's performance.

37. Calculate electrical energy input if $V = 12\,\text{V}$, $I = 2\,\text{A}$, and $t = 60\,\text{s}$.

    $1440\,\text{J}$. $E = 12 \times 2 \times 60 = 1440\,\text{J}$ using electrical energy formula.

38. Calculate average power if a device transfers $q=6000\,\text{J}$ in $t=120\,\text{s}$.

    $50\,\text{W}$. $P = \frac{6000}{120} = 50\,\text{W}$

39. What is the definition of efficiency for a thermal energy device in terms of energy transfer?

    Efficiency $=\frac{\text{useful energy out}}{\text{total energy in}}\times 100\%$. Compares useful output to total input as a percentage.

40. State the formula for thermal energy gained or lost when temperature changes.

    $Q=mc\Delta T$. Heat energy depends on mass, specific heat capacity, and temperature change.

41. Identify the best measurable indicator of heat loss from a device during a water-heating test.

    Input energy $-$ energy gained by water (difference in joules). Heat loss equals energy supplied minus energy absorbed by water.

42. What is the formula for percent error when comparing a measured value to an accepted value?

    $\%\text{ error} = \frac{|\text{measured} - \text{accepted}|}{\text{accepted}} \times 100\%$. Compares experimental result to known standard value.

43. Identify one key controlled variable when comparing two heaters using the same beaker of water.

    Water mass (volume). Keep water amount constant to ensure fair comparison.

44. State the formula for efficiency using energy values.

    $\text{Efficiency} = \frac{\text{useful energy out}}{\text{total energy in}}$. Ratio of output to input gives efficiency as a decimal.

45. Calculate power: a device transfers $240\ \text{J}$ in $60\ \text{s}$. What is $P$?

    $P=4\ \text{W}$. Use $P = \frac{240}{60} = 4$ watts.

46. Which option is the best control variable when comparing two thermal devices fairly?

    Keep the same input energy source and same test conditions (same $m$, same start $T$). Fair comparison requires identical test conditions except the device being tested.

47. What does a negative value of $Q$ indicate in a thermal energy calculation?

    thermal energy was lost by the object. Negative Q means heat flows out of the system, cooling it down.

48. Find the electrical energy input if a heater runs at $60\,\text{W}$ for $120\,\text{s}$.

    $7200\,\text{J}$. $E = 60\,\text{W} \times 120\,\text{s} = 7200\,\text{J}$

49. What is the formula for the average power output during a heating or cooling test?

    $P = \frac{q}{t}$. Power equals energy transferred divided by time taken.

50. What is the dependent variable when comparing thermal devices by heating water?

    Measured temperature change or energy gained by the water. The variable you measure to assess device performance.

51. Calculate $\Delta T$: water starts at $20^\circ\text{C}$ and ends at $35^\circ\text{C}$.

    $\Delta T=15^\circ\text{C}$. Temperature change is final minus initial: $35 - 20 = 15$.

52. Which option is the correct unit for heat energy $Q$ in $Q = mc\Delta T$?

    Joules (J). SI unit for energy, including heat energy.

53. Choose the correct conclusion: Device 1 heats water $8^{\circ}\text{C}$; Device 2 heats $5^{\circ}\text{C}$ using the same time and water mass.

    Device 1 has higher heating performance. Greater temperature rise with same conditions indicates better heating.

54. Calculate electrical power for $V = 12\,\text{V}$ and $I = 2.0\,\text{A}$.

    $24\,\text{W}$. $P = 12\,\text{V} \times 2.0\,\text{A} = 24\,\text{W}$

55. What is the formula for electrical power using voltage and current?

    $P = VI$. Power equals voltage times current in electrical circuits.

56. Identify the best instrument to measure time for a heating or cooling trial.

    Stopwatch or timer. Measures duration for calculating power or heating rate.

57. State the formula for power when you know energy transferred and time.

    Power $P=\frac{E}{t}$. Power equals energy divided by time.

58. What is the input energy if $P = 60\,\text{W}$ and $t = 120\,\text{s}$?

    $7200\,\text{J}$. Multiply power by time: $60\,W \times 120\,s = 7200\,J$.

59. Choose the correct conclusion if two trials give $\text{efficiency}=40\%$ and $41\%$ for the same device.

    Results are consistent (high precision). Close values indicate reproducible results with low random error.

60. Calculate efficiency when $E_{\text{useful out}} = 600\ \text{J}$ and $E_{\text{in}} = 800\ \text{J}$.

    $75\%$. $\text{Efficiency} = \frac{600}{800} \times 100\% = 75\%$

61. What is the efficiency if useful energy out is $400\,\text{J}$ and total energy in is $800\,\text{J}$?

    $50\%$. Apply efficiency formula: $\frac{400}{800} \times 100\% = 50\%$.

62. What is the formula for energy input from an electric heater using voltage, current, and time?

    $E_{\text{in}} = VIt$. Electrical energy equals voltage times current times time.

63. Find $Q$ for water if $m = 0.50\,\text{kg}$, $c = 4200\,\frac{\text{J}}{\text{kg}\cdot^{\circ}\text{C}}$, and $\Delta T = 10\,^{\circ}\text{C}$.

    $2.1\times10^4\,\text{J}$. $Q = 0.50 \times 4200 \times 10 = 21000$ J.

64. What measurable criterion describes how fast a device transfers thermal energy?

    Power (rate of energy transfer). Power measures energy transferred per unit time.

65. Which measurable criterion best indicates how fast a thermal device heats something?

    Heating rate (temperature change per time). Shows how quickly temperature increases over time.

66. Find and correct the calculation error: Efficiency $= \frac{1200\,\text{J}}{800\,\text{J}} \times 100\% = 150\%$ for a heater.

    Correct: efficiency cannot exceed $100\%$; inputs and outputs are reversed. Output cannot exceed input; efficiency must be ≤ 100%.

67. What measurable criterion compares useful energy output to energy input?

    Efficiency. Ratio shows how much input energy becomes useful output.

68. Calculate power when a device transfers $1200\ \text{J}$ of energy in $60\ \text{s}$.

    $20\ \text{W}$. $P = \frac{1200}{60} = 20\ \text{W}$

69. Identify the best measurable criterion to compare two heaters fairly in the same setup.

    Efficiency (useful heat gained per energy input), in $\%$. Efficiency compares output to input, making comparison fair.

70. Calculate $\%\text{ error}$ if measured power is $48\,\text{W}$ and accepted power is $50\,\text{W}$.

    $4\%$. $\%\text{ error} = \frac{|48-50|}{50} \times 100\% = 4\%$

71. Which measuring tool is most appropriate for recording $T_i$ and $T_f$ in a thermal test?

    Thermometer or temperature probe. Measures temperature accurately for thermal calculations.

72. A heater uses $500\ \text{J}$ and water gains $350\ \text{J}$. What is the wasted energy?

    Wasted energy $=150\ \text{J}$. Energy lost equals input minus useful output: $500 - 350 = 150$ J.

73. What is the definition of performance for a thermal energy device in a test?

    How well it transfers or converts thermal energy by measured criteria. Performance measures effectiveness against specific standards.

74. What is the SI unit of power $P$ when comparing thermal devices?

    Watt (W). One watt equals one joule per second.

75. What is the correct unit for energy in performance calculations such as $Q$ or $E_{\text{in}}$?

    Joules (J). SI unit for all forms of energy, including thermal and electrical.

76. Which constant value is commonly used for water in $Q=mc\Delta T$ with $m$ in grams?

    $c\approx 4.18\ \text{J}/(\text{g}\cdot ^\circ\text{C})$. Water's specific heat capacity in J/(g·°C).

77. State the formula for efficiency as a percent using energy values.

    $\text{Efficiency(\%)}=\frac{E_{\text{useful}}}{E_{\text{in}}}\times 100$. Multiply the ratio by 100 to convert decimal efficiency to percentage.

78. What is the formula for power when a device transfers energy over time?

    $P=\frac{E}{t}$. Power measures the rate of energy transfer per unit time.

79. What is the definition of power for a device transferring thermal energy?

    Power $P = \frac{E}{t}$ (rate of energy transfer). Energy transferred per unit time.

80. Which measuring tool is most appropriate for finding $m$ in $Q = mc\Delta T$ during a lab test?

    Balance or digital scale. Measures mass precisely for thermal energy calculations.

81. What is the correct SI unit for thermal energy $q$ in performance testing?

    Joules (J). SI unit for energy; thermal energy is a form of energy.

82. What does each symbol represent in $Q=mc\Delta T$ for a water-heating test?

    $Q$ energy, $m$ mass, $c$ specific heat, $\Delta T$ temp change. Variables for calculating thermal energy transfer.

83. What is the formula for electrical energy input to a heater using power and time?

    $E_{\text{in}} = Pt$. Electrical energy equals power multiplied by time.

84. What is the independent variable when testing how insulation thickness affects heat loss?

    Insulation thickness. The variable you change (thickness) to test its effect.

85. What is the formula for average power output during a thermal device test?

    $P = \frac{E}{t}$. Energy divided by time gives the rate of energy transfer.

86. What is $\Delta T$ if $T_{\text{initial}} = 20^\circ\text{C}$ and $T_{\text{final}} = 65^\circ\text{C}$?

    $45^\circ\text{C}$. Subtract initial from final: $65°C - 20°C = 45°C$.

87. What does the efficiency of a thermal energy device measure in a performance test?

    Useful energy output compared to energy input. Efficiency shows how much input energy becomes useful work.

88. Which two quantities must be measured to find heat transferred to water?

    Mass of water and temperature change. Use $Q = mc\Delta T$ where $m$ is mass and $\Delta T$ is temperature change.

89. What is the correct formula for percent error when comparing measured and accepted values?

    $\%\text{ error} = \frac{|\text{measured}-\text{accepted}|}{\text{accepted}}\times 100\%$. Absolute difference over accepted value gives relative error.

90. What is the definition of a measurable criterion in a thermal device performance test?

    A quantitative measure used to judge device performance. Measurable criteria must be numerical for objective comparison.

91. What does $\Delta T$ represent in the equation $Q = mc\Delta T$?

    $\Delta T = T_{\text{final}} - T_{\text{initial}}$. Temperature change is the difference between final and initial temperatures.

92. What is the formula for temperature change when testing a thermal energy device?

    $\Delta T = T_f - T_i$. Final temperature minus initial temperature gives the change.

93. Calculate $\Delta T$ if $T_{\text{initial}} = 20\,^{\circ}\text{C}$ and $T_{\text{final}} = 65\,^{\circ}\text{C}$.

    $45\,^{\circ}\text{C}$. $\Delta T = 65 - 20 = 45$ degrees Celsius.

94. What measurable criterion describes how well a thermal device prevents heat from escaping?

    Heat loss rate (cooling rate) to surroundings. Lower heat loss means better insulation performance.

95. Calculate efficiency if $E_{\text{useful out}}=8000\,\text{J}$ and $E_{\text{total in}}=10000\,\text{J}$.

    $80\%$. $\text{Efficiency} = \frac{8000}{10000} \times 100\% = 80\%$

96. What is the formula for electrical power input to a thermal device using voltage and current?

    $P_{\text{in}} = VI$. Electrical power equals voltage times current.

97. Which measurement tool is most appropriate for measuring mass in a thermal device test?

    Balance or scale. Measures mass of water or materials tested.

98. Which option best describes a controlled variable in a fair heater comparison test?

    Same water mass, same starting temperature, same container, same time. Keep all factors constant except the one being tested.

99. State the formula for thermal energy change when mass, specific heat, and temperature change are known.

    Thermal energy $Q=mc\Delta T$. Heat gained depends on mass, specific heat capacity, and temperature rise.

100. Calculate efficiency if useful heat gained is $6000\,\text{J}$ and energy input is $8000\,\text{J}$.

     $75\%$. $\text{Efficiency} = \frac{6000}{8000} \times 100\% = 75\%$

101. What is a control variable that must be kept constant when comparing two heaters?

     Same water mass (and same starting temperature). Keep constants the same to ensure fair comparison.

102. State the formula for heating rate using temperature data collected during a test.

     $\text{Heating rate}=\frac{\Delta T}{\Delta t}$. Change in temperature divided by elapsed time.

103. Which measurement tool is most appropriate for tracking temperature during a thermal device test?

     Thermometer or temperature probe. Measures temperature changes during testing.

104. Which measurable quantities are required to compute electrical input energy using $E_{\text{in}} = VIt$?

     Voltage $V$, current $I$, and time $t$. These electrical measurements determine total input energy.

105. Identify the independent variable when testing how insulation thickness affects heat loss.

     Insulation thickness. The variable you change to test its effect on heat loss.

106. What units are standard for thermal energy $Q$, mass $m$, and temperature change $\Delta T$?

     $Q$ in $\text{J}$, $m$ in $\text{kg}$, $\Delta T$ in $^\circ\text{C}$ or $\text{K}$. Standard SI units ensure consistent calculations across experiments.

107. Identify the dependent variable when comparing devices by how fast water temperature increases.

     Rate of temperature increase (heating rate). The measured outcome that changes based on the independent variable.

108. Identify the best instrument to measure the mass of water in a thermal device test.

     Balance (scale). Measures mass precisely for use in $Q = mc\Delta T$.

109. What is the independent variable when testing different insulation materials on a thermal device?

     Type or thickness of insulation. The variable you change to test its effect on performance.

110. Calculate efficiency if useful heat gained is $600\,\text{J}$ and electrical energy input is $1000\,\text{J}$.

     $60\%$. Efficiency $= \frac{600}{1000} \times 100\% = 60\%$ using the efficiency formula.

111. Identify the best conclusion: Device A heats $200\ \text{g}$ by $10^\circ\text{C}$; Device B heats $200\ \text{g}$ by $15^\circ\text{C}$ in same time.

     Device B has higher heating rate (greater temperature increase per time). Device B achieves $15°C$ vs A's $10°C$ in same time, so heats faster.

112. What is the standard unit for thermal energy $Q$ used in calculations?

     joule (J). The SI unit for energy is the joule, named after James Prescott Joule.

113. What is the definition of efficiency for a thermal energy device using energy measurements?

     $\text{Efficiency} = \frac{E_{\text{useful out}}}{E_{\text{total in}}}\times 100\%$. Ratio of useful output to total input, expressed as percentage.

114. Find $\Delta T$ if water starts at $22^\circ\text{C}$ and ends at $67^\circ\text{C}$ in a heater test.

     $45\,^\circ\text{C}$. $\Delta T = 67^\circ\text{C} - 22^\circ\text{C} = 45^\circ\text{C}$

115. What is the correct unit for heating rate if temperature is in $^\circ\text{C}$ and time is in seconds?

     $^\circ\text{C}/\text{s}$. Degrees Celsius per second for temperature rate.

116. State the formula for electrical energy input to a thermal device using voltage, current, and time.

     $E = VIt$. Electrical energy equals voltage times current times time.

117. Which graph type best shows how temperature changes over time during a heating test?

     Line graph of $T$ versus $t$. Line graphs show continuous change of one variable over another.

118. What is the formula for thermal efficiency of a device using energy input and useful output?

     $\text{Efficiency} = \frac{E_{\text{useful out}}}{E_{\text{in}}} \times 100\%$. Ratio of useful energy output to total energy input, expressed as percentage.

119. Which option best describes a major source of energy loss when testing a thermal device in open air?

     Heat transfer to the surroundings by convection and radiation. Air movement and thermal radiation carry heat away from the device.

120. What is the formula for percent difference when comparing two measured results?

     $\%\text{ difference} = \frac{|A - B|}{\frac{A + B}{2}} \times 100\%$. Compares two measurements using their average as reference.

121. What is the unit for thermal energy $Q$ when using $Q = mc\Delta T$?

     Joules (J). SI unit for energy when $m$ is in kg, $c$ in J/(kg·°C), $\Delta T$ in °C.

122. Find the efficiency when $E_{\text{useful}}=600\,\text{J}$ and $E_{\text{in}}=800\,\text{J}$.

     $75\%$. $\frac{600}{800} \times 100 = 75\%$ efficiency calculation.

123. Calculate efficiency if useful output is $600\ \text{J}$ and total input is $2000\ \text{J}$.

     $30\%$. Efficiency = $\frac{600}{2000} \times 100 = 30\%$.

124. What is the correct SI unit for power $P$ when rating a thermal energy device?

     Watts (W), where $1\,\text{W} = 1\,\text{J/s}$. Power is energy per unit time, measured in joules per second.

125. Which instrument is used to measure the electrical potential difference in a thermal device test?

     Voltmeter. Measures voltage in volts for power calculations.

126. Identify the independent variable when testing how insulation thickness affects heat loss rate.

     Insulation thickness. The variable you change to test its effect on heat loss.

127. Identify the energy input for an electric heater test when $P=50\,\text{W}$ and $t=120\,\text{s}$.

     $E_{\text{in}}=Pt=6000\,\text{J}$. Energy input equals power times time for electrical devices.

128. Calculate power if a device transfers $600\,\text{J}$ in $30\,\text{s}$.

     $20\,\text{W}$. $P = \frac{600\,\text{J}}{30\,\text{s}} = 20\,\text{W}$.

129. Which measurement tool is most appropriate for measuring time during a thermal device test?

     Stopwatch or timer. Tracks duration for rate calculations.

130. What does $\Delta T$ represent in $q = mc\Delta T$ when testing a thermal device?

     Temperature change: $\Delta T = T_f - T_i$. Final temperature minus initial temperature gives the change.

131. Which option is the correct unit for power $P$ of a thermal energy device?

     Watts (W), where $1\,\text{W} = 1\,\text{J/s}$. Power is energy per second, measured in watts.

132. What measurable quantities are needed to calculate $Q=mc\Delta T$ for heated water?

     Mass $m$, specific heat $c$, and temperature change $\Delta T$. These three quantities determine thermal energy change in the formula.

133. Find and correct the formula error: $\text{Efficiency}=\frac{E_{\text{in}}}{E_{\text{useful}}}\times 100$.

     $\text{Efficiency}=\frac{E_{\text{useful}}}{E_{\text{in}}}\times 100$. The fraction was inverted; useful energy goes on top.

134. Calculate $Q$ when $m = 2\ \text{kg}$, $c = 1000\ \text{J/(kg}\cdot^\circ\text{C)}$, and $\Delta T = 5^\circ\text{C}$.

     $Q = 10000\ \text{J}$. $Q = 2 \times 1000 \times 5 = 10000\ \text{J}$

135. What is power in terms of energy transfer and time for a thermal device test?

     Power $P = \frac{E}{t}$. Power measures the rate of energy transfer per unit time.

136. Find the correct efficiency: useful energy out $=90\ \text{J}$, total energy in $=120\ \text{J}$.

     Efficiency $=75\%$. Calculate: $\frac{90}{120} \times 100\% = 75\%$.

137. State the formula for electrical power using voltage and current.

     $P = VI$. Power equals voltage times current.

138. What is the formula for thermal energy gained or lost by a substance in a test?

     $q = mc\Delta T$. Relates heat transfer to mass, specific heat capacity, and temperature change.

139. What is the formula for thermal energy gained by water in a heating test?

     $Q = mc\Delta T$. Heat energy equals mass times specific heat times temperature change.

140. Which measurable quantities are required to calculate $Q$ using $Q = mc\Delta T$?

     Mass $m$, specific heat $c$, temperature change $\Delta T$. All three quantities must be measured to calculate heat energy.

141. What does $\Delta T$ represent in $Q = mc\Delta T$?

     Temperature change, $\Delta T = T_f - T_i$. Final temperature minus initial temperature.

142. Which option best describes a measurable criterion for comparing two thermal devices fairly?

     Same input energy and same test conditions (same mass, start $T$, time). Fair comparison requires identical testing conditions.

143. Which instrument is used to measure temperature change when testing a thermal device?

     Thermometer or temperature probe. Measures temperature accurately for calculating thermal energy changes.

144. What does $\Delta T$ mean in $Q = mc\Delta T$?

     $\Delta T = T_{\text{final}} - T_{\text{initial}}$. Temperature change is final minus initial temperature.

145. Calculate percent efficiency if useful output is $150\,\text{J}$ and input is $300\,\text{J}$.

     $50\%$. $\frac{150}{300} \times 100\% = 50\%$ efficiency.

146. What does $c$ represent in $Q = mc\Delta T$ when evaluating a thermal device?

     Specific heat capacity. The amount of energy needed to raise 1 kg by 1°C.

147. Identify the better insulator: Cup A loses $10^{\circ}\text{C}$ in $20\,\text{min}$; Cup B loses $6^{\circ}\text{C}$ in $20\,\text{min}$.

     Cup B. Better insulators lose less heat, shown by smaller temperature drops.

148. What measurable criterion defines a thermal device's efficiency in general terms?

     Useful energy output divided by energy input. Efficiency compares how much energy is converted to useful work versus total input.

149. Identify the correct unit for thermal energy $Q$ in the equation $Q=mc\Delta T$.

     Joules (J). Energy is measured in joules in SI units.

150. What is the best instrument to measure the temperature change of water in a heating device test?

     Thermometer or temperature probe. Measures temperature directly with appropriate precision for water.

151. What is the definition of efficiency for a thermal energy device?

     Efficiency $= \frac{\text{useful energy out}}{\text{total energy in}} \times 100\%$. Ratio of useful output to total input, expressed as a percentage.

152. What is the formula for average power output when a device delivers energy over a time interval?

     $P = \frac{E}{t}$. Power equals energy transferred divided by time taken.

153. Find the percent error if the measured efficiency is $72\%$ and the accepted efficiency is $75\%$.

     $4\%$. $\frac{|72-75|}{75} \times 100\% = 4\%$

154. What is the formula for heat lost to the surroundings during a device test?

     $Q_{\text{lost}} = E_{\text{input}} - E_{\text{useful}}$. Total input minus useful output equals wasted energy.

155. Find the heating rate if temperature rises $30^\circ\text{C}$ in $10\ \text{min}$.

     $3\ ^\circ\text{C}/\text{min}$. Rate = $\frac{30^\circ\text{C}}{10\ \text{min}} = 3\ ^\circ\text{C}/\text{min}$.

156. Calculate efficiency if $E_{\text{useful}} = 800\,\text{J}$ and $E_{\text{input}} = 2000\,\text{J}$.

     $40\%$. $\frac{800}{2000} \times 100$ efficiency.

157. Which option best indicates greater performance if two devices use equal input energy: higher or lower efficiency?

     Higher efficiency. More useful output per unit input indicates better device performance.

158. Calculate $Q$ for $m = 0.20\,\text{kg}$, $c = 4200\,\text{J/(kg}\cdot^\circ\text{C)}$, $\Delta T = 10^\circ\text{C}$.

     $8400\,\text{J}$. $Q = 0.20 \times 4200 \times 10 = 8400\,\text{J}$

159. State the formula for percent efficiency.

     $\%\text{ efficiency} = \frac{\text{useful energy out}}{\text{total energy in}} \times 100\%$. Multiply by 100 to convert decimal efficiency to percentage.

160. Calculate power if a device transfers $900\,\text{J}$ in $30\,\text{s}$.

     $30\,\text{W}$. $P = \frac{900}{30} = 30\,\text{W}$ using power equals energy over time.

161. State the formula for thermal energy gained by water in a device performance test.

     $Q=mc\Delta T$. Calculates thermal energy from mass, specific heat, and temp change.

162. Which measurable criterion best indicates reduced heat loss in an insulated container test?

     smaller temperature decrease over the same time. Good insulation slows heat transfer, maintaining temperature longer.

163. What is a fair test criterion when comparing two thermal devices?

     Keep all variables constant except the device being tested. Controlling variables ensures valid comparison between devices.

164. Choose the word that best completes the statement: A device with less energy lost to surroundings is more ____.

     Efficient. Less energy wasted means higher efficiency.

165. Calculate $\Delta T$ if water warms from $18^\circ\text{C}$ to $43^\circ\text{C}$.

     $25^\circ\text{C}$. $\Delta T = 43°C - 18°C = 25°C$

166. State the formula for efficiency as a percent when testing a thermal energy device.

     $\text{Efficiency(\%)}=\frac{\text{useful output}}{\text{total input}}\times 100$. Ratio of useful work to total energy, expressed as percentage.

167. Identify what $E_{\text{useful}}$ means in the efficiency formula for a thermal device.

     Energy transferred to the intended output (wanted energy). The portion of input energy that accomplishes the desired task.

168. What is the formula for electrical energy input when a device uses electricity?

     $E_{\text{in}} = Pt$. Electrical energy equals power multiplied by time.

169. State the formula for efficiency when testing a thermal energy device.

     $\text{Efficiency} = \frac{E_{\text{useful}}}{E_{\text{input}}} \times 100\%$. Ratio of useful output to total input, expressed as percentage.

170. Which instruments are used to measure mass, temperature, and time in a thermal test?

     balance, thermometer, stopwatch. These tools measure the key variables in thermal energy calculations.

171. What is the correct unit for power in the equation $E_{\text{in}} = Pt$?

     Watts (W). SI unit for power, equal to joules per second.

172. Identify the dependent variable in a test where you record water temperature rise over time.

     temperature change of the water. The dependent variable changes in response to the independent variable.

173. Which option best improves reliability when testing a thermal device: one trial or three trials averaged?

     Three trials averaged. Multiple trials reduce random errors and increase data reliability.

174. What is the correct definition of a controlled variable in a thermal device performance test?

     A factor kept the same in every trial. Controlled variables ensure fair testing by eliminating other influences.

175. Identify the better insulator if Cup A cools from $60^\circ\text{C}$ to $50^\circ\text{C}$ and Cup B to $55^\circ\text{C}$ in 10 min.

     Cup B. Cup B lost only $5^\circ\text{C}$ vs Cup A's $10^\circ\text{C}$, retaining heat better.

176. Calculate the average power if a heater transfers $E=1200\,\text{J}$ in $t=60\,\text{s}$.

     $20\,\text{W}$. $P = \frac{1200}{60} = 20\,\text{W}$ using power formula.

177. Identify the best instrument to measure temperature change in a heating test.

     Thermometer or temperature probe. Measures temperature accurately for calculating $\Delta T$.

178. Which instrument is used to measure the electrical current in a thermal device test?

     Ammeter. Measures current flow in amperes for power calculations.

179. What is the formula for thermal energy gained or lost by a substance during a temperature change?

     $Q = mc\Delta T$. Heat energy depends on mass, specific heat capacity, and temperature change.

180. What is the SI unit for thermal energy $Q$ used in device performance calculations?

     Joule (J). Standard unit for energy in the metric system.

181. What is the definition of efficiency for a thermal energy device in terms of energy in and out?

     Efficiency $= \frac{\text{useful energy out}}{\text{total energy in}} \times 100\%$. Ratio of useful output to total input shows how well energy is converted.

182. Calculate efficiency: useful energy out $=60\ \text{J}$, total energy in $=100\ \text{J}$.

     Efficiency $=60\%$. Apply formula: $\frac{60}{100} \times 100\% = 60\%$.

183. Which measurable quantities are needed to calculate $Q$ using $Q = mc\Delta T$ for heated water?

     Mass $m$, specific heat $c$, and temperature change $\Delta T$. These three quantities determine the thermal energy transferred.

184. Which graph type best shows heating rate when temperature is recorded every minute?

     Line graph of temperature vs. time. Shows continuous change over time, revealing heating rate.

185. Identify the measurable criterion that describes how fast a thermal device heats a sample.

     Heating rate, such as $\frac{\Delta T}{t}$. Temperature change per unit time indicates heating speed.

186. Compute $Q$ for $m=200\ \text{g}$ of water, $c=4.18$, and $\Delta T=5^\circ\text{C}$.

     $4180\ \text{J}$. $Q = 200 \times 4.18 \times 5 = 4180\ \text{J}$.

187. State the formula for thermal energy gained or lost by a substance in a device test.

     $Q = mc\Delta T$. Relates heat transfer to mass, specific heat, and temperature change.

188. Identify the best controlled variables for comparing two heaters fairly in a water-heating test.

     Same water mass, same container, same starting $T$, same time method. Controlling all variables except heater type ensures fair comparison.

189. Identify the best controlled variables when comparing two thermal devices fairly.

     Same mass, same start $T$, same container, same time/setting. Controls ensure only device performance differs.

190. Identify the performance winner: Device A heats $200\,\text{mL}$ from $20$ to $60\,^{\circ}\text{C}$ in $120\,\text{s}$; Device B in $150\,\text{s}$.

     Device A. Device A heats faster (120s < 150s) for the same temperature change.

191. What is the power if $V = 12\,\text{V}$ and $I = 2\,\text{A}$?

     $24\,\text{W}$. Multiply voltage by current: $12\,V \times 2\,A = 24\,W$.

192. Identify which device is more efficient: A has $E_{\text{useful}}=400\ \text{J}$ from $1000\ \text{J}$; B has $300\ \text{J}$ from $600\ \text{J}$.

     Device B. A: $\frac{400}{1000}=40\%$; B: $\frac{300}{600}=50\%$; B is higher.

193. State the formula for thermal energy gained or lost when temperature changes but no phase change occurs.

     $Q = mc\Delta T$. Heat energy equals mass times specific heat times temperature change.

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