Sunlight Lifts a Weight

In the picture

1. 1The tilted photovoltaic panel standing in the sunbeam.
2. 2The red wire carrying current from the panel to the motor.
3. 3The small electric motor winding its spool.
4. 4The brass weight hanging on the thread.

Examples

• A bike dynamo: your legs push the wheel, the dynamo makes a current, and the headlamp glows.
• A phone charger: mains electricity becomes chemical energy in the battery, then light and sound when you play a video.

Quiz: Sunlight Lifts a Weight (Age 16)

1. 1

   In a chain where sunlight falls on a solar panel, the panel drives a motor, and the motor lifts a weight, what best describes what happens to the energy?

   • It is passed along the chain, taking a new form at each step
   • It stays in the same form the whole way and simply moves from part to part
   • It is used up a little at each step until there is none left at the end
2. 2

   At every stage of such a chain, a little energy escapes as heat. What does that mean for the raised weight?

   • The energy stored in the raised weight is less than the energy the sunlight delivered
   • The weight ends up with exactly the energy the sunlight delivered, because energy is conserved
   • The escaped heat is energy that has been destroyed, so there is less energy in total than before
3. 3

   Once the motor has finished raising the weight and it hangs still, what form is the transferred energy in?

   • Gravitational potential energy, stored because the weight is higher up
   • Kinetic energy, because the weight travelled upwards
   • Electrical energy, still held in the weight after the motor supplied it

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.