SavemyExam Energy transfers [Hard]

Question 1

1.What is the equation of power dissipation?
2.What is the equation of power in electrical circuits?
3.What is the equation of charge of the flow?
4.What is the equation of potential difference?
5.What is the equation for energy transferred?
6.What is the equation of Ohm’s law?

Answer 1

1. Power dissipation = Current [ to the power of 2 ] x Resistance
   I = Current
   R = Resistance

2.Power = Current x Resistance

3. Charge of flow = Current x Time
   4.Potential diffrence = Current x Resistance
4. Energy transferred = Power x time
5. Potential difference = Current x Resistance

Question 2

The power rating of a washing machine is 2200W.

Calculate the total resistance of the circuit in the washing machine[4]

Answer 2

Determine the current
P = V x I
I = P/V
I= 2200/230[1]
9.6A[1]
Determine the resistance
V = I x R
R= V/I
R = 230/9.6[1]
R = 24 Ohm[1]

Question 3

A microwave has a power rating of 1000W

The kettle in Table 1 takes two minutes to boil a mug of cold water from the tap. [ power rating of kettle = 2500W]

Determine how long it would take to boil a mug of tap water in the microwave. [4]

Answer 3

Determine the energy transferred from the kettle to the water.
E = P x t
E = 2500 x [2 x60] [1]
E = 300,000J[1]
Determine the time taken to transfer the same amount of energy
t = E/P
t = 300,000/1000[1]
t = 300s[1]

Question 4

The cost of electricity is 37p per kilowatt hour [ kW hr ]

Calculate the cost of using the TV in Table 1 for 4 hours. [ TV power rating 125W] [3]

Answer 4

Determine the cost per W hr;
37/1 kW hr x 1kW/1000W = 0.037p
Determine the cost of using the Tv for 4 hours:
Cost = 0.0037 x 4
Cost = 18.5p

Question 5

Physics and math tutour

A householder always fills the electric kettle to the top, even when only enough
boiling water for one small cup of coffee is wanted.
Explain how the householder is wasting money.

Answer 5

The greater the volume the more it takes time to boil.[1]
so more energy is transferred[1]
and this costs more[1]

Question 6

Physics and math tutour

The electrician should not change the shower unless he switches off the mains
electricity supply.
Explain why. [2]

Answer 6

He may receive an electric shock[1]
if he touches a live wire [1]