Energy transfers (2.4) (M)

Question 1

The greater the current/potential difference, the (…) the power transfer in the circuit

Answer 1

greater

Question 2

Everyday electrical appliances are designed to bring about what?

Answer 2

energy transfers

Question 3

The longer you leave a light bulb on, the (..) the energy is used

Answer 3

greater

Question 4

2 things

The amount of energy an appliance transfers depends on what?

Answer 4

how long the appliance is switched on for and the power of the appliance

P = E/t

Question 5

How do different domestic appliances transfer energy from batteries or ac mains to the kinetic energy of electric motors or the energy of heating devices

Answer 5

from chemical store of batteries/electrical store of ac supply to thermal/kinetic store of heating device/electrical motor via work done when current flows

Question 6

When is work done in a circuit?

Answer 6

when charge flows

Question 7

The greater the voltage/charge, the (…) the energy transferred/work done.

Answer 7

greater

Question 8

Describe the relationship between an appliance with a higher power rating and changes in energy store

Answer 8

A device with a higher power rating will transfer stored energy to other types of energy at a faster rate

Question 9

What are some common power ratings of domestic electrical appliances?

Answer 9

• A kettle is typically 3kW (3000W)*
• A microwave 900W*
• A lightbulb 10W*
• Every appliance in your home will have a power rating on it.*

Question 10

What is the National Grid?

Answer 10

a system of cables and transformers linking power stations to consumers

National grid only consists from step-up transformer to step-down transformer (does not include houses/power station)

Question 11

What is used to transfer electrical power from power stations to consumers?

Answer 11

the National Grid

Question 12

What does a step-up transformer do?

Answer 12

Increase voltage, decrease current

Question 13

What does a step-down transformer do?

Answer 13

decrease voltage, increase current

Question 14

What is the role of step-up transformers in the National Grid?

Answer 14

Step-up transformers are used to increase the potential difference (to a very high voltage) from the power station to the transmission cables for efficient transmission

also means thinner wires can be used and less power is lost as P = I₂R - add high current stuff to this answer if asked in an exam

Question 15

What is the role of step-down transformers in the National Grid?

Answer 15

Step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use (as high voltage is unsafe)

Question 16

Why do transmission cables not have a high current?

Answer 16

If you have a big current then the wires will get hot and lots of (thermal) energy will be wasted

therefore it is very inefficient

so they transmit it at a very high voltage as it makes up the majority of the distance of transmission

Question 17

The National Grid is an (…) way to transfer energy

Answer 17

efficient

Question 18

Why is there not a high voltage for domestic appliances?

Answer 18

A high voltage is unsafe - would be fatal

Question 19

Why could an 18V battery not be used at the input of a transformer?

Answer 19

Need a.c.

Battery is d.c.

Question 20

Why does the resistance of bulb increase as pd increases across the bulb?

Answer 20

Temperature of bulb increases

Question 21

2 marks

A small community in the area live in the mountains.

Why would it not be economical to connect them to the national grid?

Answer 21

• high cost of installing overhead power lines or underground cables or pylons
• high cost as (very) long cables needed
• amount of electricity required is too low

Question 22

4 marker

A man touches a live wire, he experiences an electrical shock, explain why?

Answer 22

The potential difference of the man is 0V

The potential difference of the live wire is 230V

So there is a large potential difference between the man and live wire

so charge passes through his body

top two points unlikely to be needed, possibly need to know bottom two though

Question 23

What does potential difference mean?

Answer 23

The work done/energy transferred per coulomb of charge

Question 24

3 marks

Why does the resistance of a metal filament inside a bulb increase as pd increases?

Answer 24

Metals contain free electrons

As the temperature of the filament increases, the ions vibrate faster

so electrons collide more frequently with ions

Question 25

What is the action and purpose of a solar panel?

Answer 25

Water heated by radiation (from Sun)

Water used to heat buildings