Save my exam Energy transfers [ Easy]

Question 1

Why would it be dangerous for the live wire from the electric cable to touch the case of the toaster[1]

Answer 1

There is a risk of electric shock if somebody touches the case[1]

Question 2

The toaster uses mains power to function.

A label on the toaster says that the power output of the toaster is 1.5kW.

Calculate the current in the toaster. [3]

Answer 2

The Uk main supply is an ac supply at around 230 V.
Power = Current x Voltage
1500= I x 230[1]
I=1500/230[1]
I= 6.52 A[1]

Question 3

Calculate the resistance of the toaster [3]

Answer 3

V = I x R
230=6.52 x R
230/6.52[1]
R= 35 (.3) Ohm

Question 4

What is th correct equation linking power, current and resistance?

Answer 4

P = I ( to the power of 2) x R

Question 5

A homeowner buys an electrical heater with a maximum power rating of 2000W.

She wants to know if it uses more energy to put the heater on full power for 1 hour or to put it on half power for 2 hours

Show that the energy transferred in both cases will be the same. [6]

Answer 5

Energy transferred = Power x time
Time = 1h = 60 min x 60 min = 3600s
E = 2000 x 3600
E = 7200,000J

Power = 1000W
Time = 2hr = 2x 3600s = 7200s
E = 1000x 7200
E= 7200,000J