Revision on Power in Electric Circuits

What do you see in the diagram?

• Mr. Coulomb

• The red bag containing energy

• Light bulb

• Battery

Where does Mr. Coulomb gain energy in this circuit?

• Battery

• Light bulb

Read this carefully:

"Mr. Coulomb has +1 C of charge. When he moves past the battery, he gains energy equal to 3 J."

and

"The emf is also 3 V."

What do you think emf means?

• emf is the energy gained per amount of charge when moving through the cell.

• emf is the amount of charge per energy gained when moving through the cell.

Where does Mr. Coulomb lose energy?

• Battery

• Light bulb

Read this carefully:

"Mr. Coulomb loses 3 J when he walks past the bulb. The pd across the bulb is 3 V."

What is potential difference (pd)?

• pd is the energy lost to the equipment per amount of charge when moving through the equipment.

• pd is the amount of charge per energy lost to the equipment when moving through the equipment.

Mr. Coulomb works in two different scenarios:

Scenario A: He delivers 6 J of energy in 2 seconds.

Scenario B: He delivers 6 J of energy in 1 second.

Which scenario does Mr. Coulomb do work at a faster rate?

The rate of doing work is called POWER.

• Scenario A

• Scenario B

Which formula correctly describes power?

Now let's focus on the light bulb. In every second, Mr. Coulomb carries electrical energy of 10 J and gives this to the bulb. Once the bulb receives the energy, it converts this energy to light of 2 J and thermal energy (heat) of 8 J. The input energy in this situation is ​ (a)   .

The useful energy in this situation is ​ (b)   . The wasted energy is ​ (c)   .

• electrical energy
• light
• heat

• 0.2

• 0.8

• 5

A toaster uses 1000 J of electrical energy. It produces 750 J of heat and 250 J of light energy. What is the wasted form of energy in this toaster?

• Heat

• Light