Evaluate Device Energy Efficiency - Physics
Card 1 of 30
What is the formula for efficiency in terms of useful output energy and total input energy?
What is the formula for efficiency in terms of useful output energy and total input energy?
Tap to reveal answer
$\text{efficiency}=\frac{E_\text{useful}}{E_\text{input}}$. Ratio of useful output to total input energy.
$\text{efficiency}=\frac{E_\text{useful}}{E_\text{input}}$. Ratio of useful output to total input energy.
← Didn't Know|Knew It →
What is the formula for percentage efficiency using useful output energy and total input energy?
What is the formula for percentage efficiency using useful output energy and total input energy?
Tap to reveal answer
$%\text{ efficiency}=\frac{E_\text{useful}}{E_\text{input}}\times 100%$. Multiply efficiency ratio by 100 to get percentage.
$%\text{ efficiency}=\frac{E_\text{useful}}{E_\text{input}}\times 100%$. Multiply efficiency ratio by 100 to get percentage.
← Didn't Know|Knew It →
Identify the more efficient device: A has $%\text{ efficiency}=85%$, B has $%\text{ efficiency}=0.90\times 100%$.
Identify the more efficient device: A has $%\text{ efficiency}=85%$, B has $%\text{ efficiency}=0.90\times 100%$.
Tap to reveal answer
Device B. B has 90% efficiency, higher than A's 85%.
Device B. B has 90% efficiency, higher than A's 85%.
← Didn't Know|Knew It →
Which option correctly gives the relation between efficiency and wasted fraction of input energy?
Which option correctly gives the relation between efficiency and wasted fraction of input energy?
Tap to reveal answer
$\text{wasted fraction}=1-\text{efficiency}$. If efficiency is 0.7, then 0.3 (30%) is wasted.
$\text{wasted fraction}=1-\text{efficiency}$. If efficiency is 0.7, then 0.3 (30%) is wasted.
← Didn't Know|Knew It →
What is the wasted power if $P_\text{input}=200,\text{W}$ and $\text{efficiency}=0.65$?
What is the wasted power if $P_\text{input}=200,\text{W}$ and $\text{efficiency}=0.65$?
Tap to reveal answer
$70,\text{W}$. $P_\text{wasted} = 200 - (200 \times 0.65) = 70,\text{W}$
$70,\text{W}$. $P_\text{wasted} = 200 - (200 \times 0.65) = 70,\text{W}$
← Didn't Know|Knew It →
What is the formula for efficiency in terms of useful output power and total input power?
What is the formula for efficiency in terms of useful output power and total input power?
Tap to reveal answer
$\text{efficiency}=\frac{P_\text{useful}}{P_\text{input}}$. Same ratio applies to power as to energy.
$\text{efficiency}=\frac{P_\text{useful}}{P_\text{input}}$. Same ratio applies to power as to energy.
← Didn't Know|Knew It →
Find the efficiency if a device outputs $900,\text{J}$ useful energy from $1.2,\text{kJ}$ input energy.
Find the efficiency if a device outputs $900,\text{J}$ useful energy from $1.2,\text{kJ}$ input energy.
Tap to reveal answer
$0.75$. $\text{efficiency} = \frac{900}{1200} = 0.75$
$0.75$. $\text{efficiency} = \frac{900}{1200} = 0.75$
← Didn't Know|Knew It →
What is the percentage efficiency if $P_\text{useful}=18,\text{W}$ and $P_\text{input}=24,\text{W}$?
What is the percentage efficiency if $P_\text{useful}=18,\text{W}$ and $P_\text{input}=24,\text{W}$?
Tap to reveal answer
$75%$. $\frac{18}{24}\times 100% = 75%$
$75%$. $\frac{18}{24}\times 100% = 75%$
← Didn't Know|Knew It →
What is the useful output power if $P_\text{input}=500,\text{W}$ and $%\text{ efficiency}=30%$?
What is the useful output power if $P_\text{input}=500,\text{W}$ and $%\text{ efficiency}=30%$?
Tap to reveal answer
$150,\text{W}$. $P_\text{useful} = 500 \times 0.30 = 150,\text{W}$
$150,\text{W}$. $P_\text{useful} = 500 \times 0.30 = 150,\text{W}$
← Didn't Know|Knew It →
What is the input power if $%\text{ efficiency}=80%$ and $P_\text{useful}=120,\text{W}$?
What is the input power if $%\text{ efficiency}=80%$ and $P_\text{useful}=120,\text{W}$?
Tap to reveal answer
$150,\text{W}$. $P_\text{input} = \frac{120}{0.80} = 150,\text{W}$
$150,\text{W}$. $P_\text{input} = \frac{120}{0.80} = 150,\text{W}$
← Didn't Know|Knew It →
Identify the correct statement about energy in a device: $E_\text{input}$, $E_\text{useful}$, and $E_\text{wasted}$.
Identify the correct statement about energy in a device: $E_\text{input}$, $E_\text{useful}$, and $E_\text{wasted}$.
Tap to reveal answer
$E_\text{input}=E_\text{useful}+E_\text{wasted}$. Energy conservation: input equals useful plus wasted.
$E_\text{input}=E_\text{useful}+E_\text{wasted}$. Energy conservation: input equals useful plus wasted.
← Didn't Know|Knew It →
What is the formula for wasted energy in terms of input energy and useful output energy?
What is the formula for wasted energy in terms of input energy and useful output energy?
Tap to reveal answer
$E_\text{wasted}=E_\text{input}-E_\text{useful}$. Energy not converted to useful form is wasted.
$E_\text{wasted}=E_\text{input}-E_\text{useful}$. Energy not converted to useful form is wasted.
← Didn't Know|Knew It →
What is the wasted energy if $E_\text{input}=500,\text{J}$ and $E_\text{useful}=350,\text{J}$?
What is the wasted energy if $E_\text{input}=500,\text{J}$ and $E_\text{useful}=350,\text{J}$?
Tap to reveal answer
$150,\text{J}$. $E_\text{wasted} = 500 - 350 = 150,\text{J}$
$150,\text{J}$. $E_\text{wasted} = 500 - 350 = 150,\text{J}$
← Didn't Know|Knew It →
What is the total input energy if $E_\text{useful}=150,\text{J}$ and $\text{efficiency}=0.60$?
What is the total input energy if $E_\text{useful}=150,\text{J}$ and $\text{efficiency}=0.60$?
Tap to reveal answer
$250,\text{J}$. $E_\text{input} = \frac{150}{0.60} = 250,\text{J}$
$250,\text{J}$. $E_\text{input} = \frac{150}{0.60} = 250,\text{J}$
← Didn't Know|Knew It →
What is the useful output energy if $\text{efficiency}=0.30$ and $E_\text{input}=200,\text{J}$?
What is the useful output energy if $\text{efficiency}=0.30$ and $E_\text{input}=200,\text{J}$?
Tap to reveal answer
$60,\text{J}$. $E_\text{useful} = 0.30 \times 200 = 60,\text{J}$
$60,\text{J}$. $E_\text{useful} = 0.30 \times 200 = 60,\text{J}$
← Didn't Know|Knew It →
What is the efficiency if $P_\text{useful}=45,\text{W}$ and $P_\text{input}=60,\text{W}$?
What is the efficiency if $P_\text{useful}=45,\text{W}$ and $P_\text{input}=60,\text{W}$?
Tap to reveal answer
$0.75$. $\frac{45}{60} = 0.75$
$0.75$. $\frac{45}{60} = 0.75$
← Didn't Know|Knew It →
What is the percentage efficiency if $E_\text{useful}=60,\text{J}$ and $E_\text{input}=80,\text{J}$?
What is the percentage efficiency if $E_\text{useful}=60,\text{J}$ and $E_\text{input}=80,\text{J}$?
Tap to reveal answer
$75%$. $\frac{60}{80}\times 100% = 75%$
$75%$. $\frac{60}{80}\times 100% = 75%$
← Didn't Know|Knew It →
Identify the correct unit for efficiency (not percentage efficiency).
Identify the correct unit for efficiency (not percentage efficiency).
Tap to reveal answer
No unit (dimensionless ratio). Efficiency is a ratio of same units, so they cancel.
No unit (dimensionless ratio). Efficiency is a ratio of same units, so they cancel.
← Didn't Know|Knew It →
Which option correctly states the allowed range of efficiency values (as a decimal) for real devices?
Which option correctly states the allowed range of efficiency values (as a decimal) for real devices?
Tap to reveal answer
$0\leq \text{efficiency}\leq 1$. Efficiency cannot exceed 1 (100%) due to energy conservation.
$0\leq \text{efficiency}\leq 1$. Efficiency cannot exceed 1 (100%) due to energy conservation.
← Didn't Know|Knew It →
What is the formula for percentage efficiency using useful output power and total input power?
What is the formula for percentage efficiency using useful output power and total input power?
Tap to reveal answer
$%\text{ efficiency}=\frac{P_\text{useful}}{P_\text{input}}\times 100%$. Multiply power ratio by 100 for percentage.
$%\text{ efficiency}=\frac{P_\text{useful}}{P_\text{input}}\times 100%$. Multiply power ratio by 100 for percentage.
← Didn't Know|Knew It →
Calculate the efficiency when $E_{\text{useful}}=60,\text{J}$ and $E_{\text{in}}=100,\text{J}$.
Calculate the efficiency when $E_{\text{useful}}=60,\text{J}$ and $E_{\text{in}}=100,\text{J}$.
Tap to reveal answer
$0.60$ (or $60%$). Apply $\text{efficiency}=\frac{60}{100}=0.60$.
$0.60$ (or $60%$). Apply $\text{efficiency}=\frac{60}{100}=0.60$.
← Didn't Know|Knew It →
Identify the correct relation between power, energy, and time used to find input power.
Identify the correct relation between power, energy, and time used to find input power.
Tap to reveal answer
$P=\frac{E}{t}$. Power equals energy divided by time.
$P=\frac{E}{t}$. Power equals energy divided by time.
← Didn't Know|Knew It →
Which option is the correct unit for power used in efficiency calculations: $\text{J}$ or $\text{W}$?
Which option is the correct unit for power used in efficiency calculations: $\text{J}$ or $\text{W}$?
Tap to reveal answer
$\text{W}$. Watt (W) is the SI unit for power.
$\text{W}$. Watt (W) is the SI unit for power.
← Didn't Know|Knew It →
Which option is the correct unit for energy used in efficiency calculations: $\text{J}$ or $\text{W}$?
Which option is the correct unit for energy used in efficiency calculations: $\text{J}$ or $\text{W}$?
Tap to reveal answer
$\text{J}$. Joule (J) is the SI unit for energy.
$\text{J}$. Joule (J) is the SI unit for energy.
← Didn't Know|Knew It →
What is the formula for wasted power in terms of total input and useful output power?
What is the formula for wasted power in terms of total input and useful output power?
Tap to reveal answer
$P_{\text{wasted}}=P_{\text{total in}}-P_{\text{useful out}}$. Same principle applies to power: input minus output equals waste.
$P_{\text{wasted}}=P_{\text{total in}}-P_{\text{useful out}}$. Same principle applies to power: input minus output equals waste.
← Didn't Know|Knew It →
Identify the term for energy that is not transferred to the intended output of a device.
Identify the term for energy that is not transferred to the intended output of a device.
Tap to reveal answer
Wasted energy. Energy lost as heat, sound, or other unwanted forms.
Wasted energy. Energy lost as heat, sound, or other unwanted forms.
← Didn't Know|Knew It →
What is the formula for wasted energy in terms of total input and useful output energy?
What is the formula for wasted energy in terms of total input and useful output energy?
Tap to reveal answer
$E_{\text{wasted}}=E_{\text{total in}}-E_{\text{useful out}}$. The difference between input and output gives waste.
$E_{\text{wasted}}=E_{\text{total in}}-E_{\text{useful out}}$. The difference between input and output gives waste.
← Didn't Know|Knew It →
State the formula for efficiency in terms of useful output energy and total input energy.
State the formula for efficiency in terms of useful output energy and total input energy.
Tap to reveal answer
$\text{efficiency}=\frac{E_{\text{useful out}}}{E_{\text{total in}}}$. Efficiency is the ratio of useful output to total input.
$\text{efficiency}=\frac{E_{\text{useful out}}}{E_{\text{total in}}}$. Efficiency is the ratio of useful output to total input.
← Didn't Know|Knew It →
State the formula for efficiency in terms of useful output power and total input power.
State the formula for efficiency in terms of useful output power and total input power.
Tap to reveal answer
$\text{efficiency}=\frac{P_{\text{useful out}}}{P_{\text{total in}}}$. Same ratio applies whether using energy or power values.
$\text{efficiency}=\frac{P_{\text{useful out}}}{P_{\text{total in}}}$. Same ratio applies whether using energy or power values.
← Didn't Know|Knew It →
What is the formula to convert efficiency (decimal) into percentage efficiency?
What is the formula to convert efficiency (decimal) into percentage efficiency?
Tap to reveal answer
$\text{efficiency (%)}=100\times\text{efficiency}$. Multiply decimal efficiency by 100 to get percentage.
$\text{efficiency (%)}=100\times\text{efficiency}$. Multiply decimal efficiency by 100 to get percentage.
← Didn't Know|Knew It →