Design Energy Conversion Devices - Physics

1. Calculate useful output if input is $500\ \text{J}$ and efficiency is $0.20$.

   $100\ \text{J}$. $\text{Useful}=0.20\times 500=100\ \text{J}$.

2. Which energy conversion best describes a wind turbine connected to a generator?

   Kinetic (wind) $\rightarrow$ electrical energy. Moving air spins blades connected to generator.

3. Which energy conversion best describes an electric motor in normal operation?

   Electrical energy $\rightarrow$ kinetic (mechanical) energy. Motors use electricity to create rotational motion.

4. Which energy conversion best describes an LED indicator light in a circuit?

   Electrical energy $\rightarrow$ light energy (and some thermal). Current through semiconductor emits photons efficiently.

5. State the percent efficiency formula for an energy conversion process.

   $\%\text{efficiency}=\frac{\text{useful output}}{\text{total input}}\times 100\%$. Multiply efficiency ratio by 100 to express as percentage.

6. What is the term for a device that converts mechanical rotation into electrical energy?

   Generator. Uses electromagnetic induction to produce current from rotation.

7. What energy conversion is performed by a wind turbine connected to a generator?

   Kinetic (wind) energy to electrical energy. Rotating blades turn generator shaft to induce current.

8. What is the correct expression for electrical energy transferred when power is constant for time $t$?

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

9. Which energy conversion best describes an electric generator in normal operation?

   Kinetic (mechanical) energy $\rightarrow$ electrical energy. Generators use motion to induce electrical current.

10. What is the correct expression for electrical power in a circuit using voltage and current?

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

11. Which energy conversion best describes a solar cell (photovoltaic cell)?

    Radiant (light) energy $\rightarrow$ electrical energy. Photons excite electrons to create current.

12. What is the main energy conservation rule that constrains all energy-conversion designs?

    Energy in $=$ energy out (useful $+$ wasted). Conservation of energy: total input equals total output.

13. Which design change most directly reduces wasted thermal energy from friction in moving parts?

    Lubrication (or low-friction bearings). Reduces friction forces that convert motion to heat.

14. What energy conversion is performed by a battery while powering a circuit?

    Chemical energy to electrical energy. Redox reactions create electron flow through circuit.

15. Which energy conversion best describes a loudspeaker producing sound from a signal?

    Electrical energy $\rightarrow$ sound energy. Electric current drives cone vibrations to produce sound waves.

16. What energy conversion is performed by a photovoltaic (solar) cell?

    Radiant (light) energy to electrical energy. Photons excite electrons across semiconductor junction.

17. What is the formula for efficiency in terms of useful output and total input power?

    $\text{efficiency}=\frac{P_{\text{useful out}}}{P_{\text{total in}}}$. Same ratio applies to power since $P = E/t$.

18. What energy conversion is performed by an electric resistance heater (idealized)?

    Electrical energy to thermal energy. Current through resistor dissipates energy as heat.

19. Calculate input power if efficiency is $0.40$ and useful output power is $120\,\text{W}$.

    $300\,\text{W}$. $P_{in} = P_{out}/\text{eff} = 120/0.40 = 300$ W.

20. Which energy conversion best describes a microphone (sound sensor) producing a signal?

    Sound energy $\rightarrow$ electrical energy. Sound waves vibrate diaphragm to induce electrical signal.

21. Calculate efficiency if $P_{\text{useful}}=60\,\text{W}$ and $P_{\text{in}}=80\,\text{W}$.

    $0.75$. Efficiency = $60/80 = 0.75$ using power ratio formula.

22. What energy conversion is performed by an LED when it is operating normally?

    Electrical energy to radiant (light) energy. Current through semiconductor junction emits photons.

23. What is the term for a device that converts electrical energy into mechanical rotation?

    Electric motor. Uses electromagnetic forces to create rotational motion.

24. Which option best describes a Sankey diagram in energy-device design?

    A diagram showing energy inputs, useful outputs, and wasted transfers. Width of arrows shows relative energy flow amounts.

25. What energy conversion is performed by a microphone converting sound to a signal?

    Sound energy to electrical energy. Sound waves vibrate diaphragm, inducing current in coil.

26. Identify the main wasted energy output to reduce when designing a more efficient electric motor.

    Thermal energy from resistive heating and friction. These losses reduce motor efficiency below 100%.

27. Identify the term for output energy that is not intended in a device (often to surroundings).

    Wasted energy (dissipated energy). Energy lost to heat, sound, or other unwanted forms.

28. What is the formula for efficiency in terms of useful output and total input energy?

    $\text{efficiency}=\frac{E_{\text{useful out}}}{E_{\text{total in}}}$. Ratio of useful output to total input energy.

29. What is the definition of efficiency for an energy-converting device?

    $\text{efficiency}=\frac{\text{useful energy out}}{\text{total energy in}}$. Ratio shows how much input energy becomes useful output.

30. Calculate wasted power if $P_{\text{in}}=500\,\text{W}$ and efficiency is $0.70$.

    $150\,\text{W}$. $P_{waste} = P_{in} - P_{out} = 500 - (0.70 × 500) = 150$ W.

31. What is the term for a device that changes energy from one form to another?

    Energy transducer (energy converter). Converts energy between different forms like electrical to mechanical.

32. Which energy conversion best describes a hydroelectric dam power station?

    Gravitational potential $\rightarrow$ electrical energy. Falling water turns turbines to generate electricity.

33. Calculate efficiency if a motor gets $80\ \text{J}$ in and delivers $60\ \text{J}$ useful out.

    $0.75$ (or $75\%$). $\text{Efficiency}=\frac{60}{80}=0.75$ or $75\%$.

34. Identify the correct unit for power used when evaluating energy-conversion devices.

    Watt (W). SI unit for power is joules per second.

35. What energy conversion is performed by a loudspeaker playing sound from an audio signal?

    Electrical energy to sound energy. Current through coil creates magnetic field that moves cone.

36. Which energy conversion best describes a battery powering a flashlight bulb?

    Chemical energy $\rightarrow$ electrical $\rightarrow$ light (and thermal). Battery chemistry powers circuit; bulb converts electricity to light.

37. Which single component should you choose to convert electrical energy into motion in a device?

    Electric motor. Designed specifically to convert electrical to mechanical energy.

38. Calculate wasted energy if input is $120\ \text{J}$ and useful output is $90\ \text{J}$.

    $30\ \text{J}$. $\text{Wasted}=120-90=30\ \text{J}$ by energy conservation.

39. Which energy conversion best describes a resistive heater (heating element)?

    Electrical energy $\rightarrow$ thermal energy. Current through resistance produces heat via Joule heating.

40. What energy conversion is performed by a hydroelectric dam and turbine-generator system?

    Gravitational potential energy to electrical energy. Falling water spins turbines connected to generators.

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