10.3 B Direct current work and power of current presentation

Voltmeters measure potential difference
2. Energy is lost in wires as heat
3. Friction is the main cause for energy loss in wires
4. Current flows from the – to the + terminal
5. Electrons carry a positive charge
6. A ammeter measures the flow of current
7. The lower the resistance the higher the voltage
8 Electrons carry energy to the component
A diode allows current flow in one direction only
10. A wide diameter wire has a low resistance

Voltmeters measure potential difference T
2. Energy is lost in wires as heat T
3. Friction is the main cause for energy loss in wires T
4. Current flows from the – to the + terminal T
5. Electrons carry a positive charge F
6. A ammeter measures the flow of current T
7. The lower the resistance the higher the voltage F
8 Electrons carry energy to the component T
A diode allows current flow in one direction only T
10. A wide diameter wire has a low resistance T

Electrical work and Power

Learning Objectives

Explain it?
What is Electrical Power?

Is the energy transferred from the electric source
to the appliance per second.

It is measured in Watts

1W is the transfer of 1 Joule per second

Power on appliances is shown as the power rating.

This is a measure of how much energy the appliance needs to work.

The higher the energy rating the more electricity (energy) it uses.

If we increase the power more light is produced.
Why?

The greater the power the more energy is transferred to light

Place these appliances in order of cost to run – most expensive first

Kettle 1800W

TV 120W

Light bulb 60W

Fridge 200W

Hair drier 1200W

Cooker 3200W

Can you find the power
rating on these appliances

Which one is the
most expensive to leave on

Electrical work and Power

Learning Objectives

P = E ÷ t

P = Power (W) Watt
E = Energy (J) Joule
t = Time (t) Seconds

E

P

t

Power = Energy ÷ time

A drill transfers 1100J of energy in 10 seconds
what is it power rating?

A fridge uses 660J of energy in 2 seconds what
is the power rating?

A 60W bulb transfers 6300J of energy, how long
was it on for?

A drill transfers 1100J of energy in 10 seconds
what is it power rating? 110W

A fridge uses 660J of energy in 2 seconds what
is the power rating? 330W

A 60W bulb transfers 6300J of energy, how long
was it on for? 105s

P = I x V

P = Power (W) Watt
I = Current (A) Amps
V = Potential Difference (V) Volts

P

I

V

Power = Current x Potential Diffrence

An Xbox has a current of 0.8A operating with a
potential difference of 230V what is the power rating.

A computer works on a potential difference of 110V and a
power rating of 65W, what is the required current.

A modem has a power of 12W and a current of 2A what
is the potential difference.

An Xbox has a current of 0.8A operating with a
potential difference of 230V what is the power rating.
184W
A computer works on a potential difference of 110v and a
power rating of 65W, what is the required current.
0.59A
A modem has a power of 12W and a current of 2A what
is the potential difference. 6V

P = I2 x R

P = Power (W) Watt
I = Current (A) Amps
R = Resistance (Ω) Ohms

P

I2

R

Power = Current2 x Resistance

An electric cooker has 1.2 amps running through it with
a resistance of 80 Ohms what is the power rating.

A fan has a power rating of 40W operating on a current
of 0.6 amps, what is its electrical resistance.

A computer runs on 0.4 amps with a resistance of 200
Ohms what is the power rating.

An electric cooker has 1.2 amps running through it with
a resistance of 80 Ohms what is the power rating. 115.2W

A fan has a power rating of 40W operating on a current
of 0.6 amps, what is its electrical resistance. 111.11 Ohms

A computer runs on 0.4 amps with a resistance of 200
Ohms what is the power rating. 32W

Energy Transferred

But we usually use it for calculating the energy transferred in circuits so it is more useful rearranged



Where:
Energy transferred is in Joules (J)
Power is in Watts (W)
Time is in seconds (s)

You must be able to recall and apply this equation

Energy transferred by appliances

Looking at the range of devices we have, complete the table
Identify the starting and finishing energy stores
Locate the power label and record the power rating of the device
Then calculate the energy transferred in one second and in 5 minutes.

The Energy - Charge Equation

Energy = charge moved x potential diffrence

E = Energy transferred (J)
Q = Charge (C)
V = potential difference (V)

E = Q x V

Energy

Charge

Potential
difference

A potential difference of 2.5 V flows through a lamp
transferring 800J of energy, how much charge flows
through the lamp.
2. How much energy is being transferred to a toaster with
a potential difference of 230V and a charge of 350C
A potential difference of 230V flows through a welder
transferring 184,000J of energy, how much charge
flows through the welder.

A potential difference of 2.5 V flows through a lamp
transferring 800J of energy, how much charge flows
through the lamp. 320C
2. How much energy is being transferred to a toaster with
a potential difference of 230v and a charge of 350C
80,500J
A potential difference of 230V flows through a welder
transferring 184,000J of energy, how much charge
flows through the welder. 800C

Calculations

Now complete the worksheet of energy transfer calculations

Power and energy transferred
The power of an appliance is the amount of energy it transfers every second.
We can write this as an equation: power (W) = energy (J) ÷ time (s)
Use this information to answer the following questions:
1. A 1500 W hairdryer is used for 10 minutes. Calculate:
a) the time it was on for, in seconds
b) the total amount of energy transferred by the hairdryer in this time.
2. An electric oven with a power rating of 2.5 kW is switched on for 45 minutes. Calculate:
a) the time it was on for, in seconds
b) the total amount of energy transferred by the oven in this time.
Charge and energy transferred
When charge flows in a circuit, electrical work is done. We can calculate the amount of energy transferred by electrical work using the equation:
energy transferred (J) = charge flow (C) × potential difference (V)
Use this equation to solve the following:
3. A charge of 30 C flows through a television that is connected to the mains supply of 230 V. Calculate the total energy transferred.
4. A device that transfers 600 J of energy has a potential difference of 12 V across it. Calculate the amount of charge that flows through the device.
5. A device transfers a total of 2000 J of energy with a charge of 50 C. Calculate the potential difference across the device.

Power and energy transferred
power (W) = energy (J) ÷ time (s)
1. A 1500 W hairdryer is used for 10 minutes. Calculate:
a) the time it was on for, in seconds 600s
b) the total amount of energy transferred by the hairdryer in this time. 900,000J
2. An electric oven with a power rating of 2.5 kW is switched on for 45 minutes. Calculate:
a) the time it was on for, in seconds 2,700s
b) the total amount of energy transferred by the oven in this time. 6,750,000J

Charge and energy transferred
energy transferred (J) = charge flow (C) × potential difference (V)
3. A charge of 30 C flows through a television that is connected to the mains supply of 230 V. Calculate the total energy transferred. 6,900J
4. A device that transfers 600 J of energy has a potential difference of 12 V across it. Calculate the amount of charge that flows through the device. 50C
5. A device transfers a total of 2000 J of energy with a charge of 50 C. Calculate the potential difference across the device. 40V

Complete your learning triangle for today.

7M6L1

1 thing I already knew

2 questions I would still like answered

3 things I have learned

Give Me

From this lesson

Now link them together to make a condensed
paragraph to describe what you have learned today