1. Use the equations P = IV and V = IR in order to derive the equation, P = I2 R.

2. Copy and complete this table:

 

 

 

 

 

 

3. What is the power rating of a lamp that has a resistance of 5 Ω and a current of 1.2 A flowing through it?

4. What is the current flowing through a 50 Ω heating element in a toaster if it has a power rating of 800 W?

5. What is the resistance of a 1200 W electric convection heater that has a current of 5.0 A flowing through it.

 

 

 

 

 

 

6. Combine the equations P = IV and I = V / R to derive the equation P = V2 / R.

7. Copy and complete this table:

 

 

 

 

 

8. What is the power rating of a mains television that has a resistance of 529 Ω?

9. What is the voltage across a portable electric shaver that has a resistance of 2.45 Ω and a power rating of 20 W?

10. What is the resistance of an 800 W mains powered coffee machine?

11. A 130 W tropical fish aquarium is connected to the mains.

(a) What is the resistance of the aquarium?

(b) What is the current flowing through the aquarium?

(c) How much energy is used up by the aquarium in 24 hours?

12. A hairdryer has three heat settings: cold, warm and hot. The hairdryer is made up of two 300 Ω resistors and a 50 Ω motor that are connected in parallel with the mains supply, as shown.

(a) What is the energy change that occurs when current flows through a resistor?

(b) Which switches are closed when the hairdryer is blowing out warm air?

(c) How much current is drawn from the mains when the hairdryer is blowing out cold air?

(d) What is the power rating of the hairdryer when it is blowing out cold air?

(e) What is the total resistance of the hairdryer when it is blowing out hot air?

(f) What is the power rating of the hairdryer when it is blowing out hot air?

(g) How much electrical energy will the hairdryer use if it blows cold air for 1 minute and hot air for 8 minutes?