Electricity

Question 1

What is the diagram for a fuse?

Answer 1

Question 2

What is the circuit symbol for a diode?

Answer 2

Question 3

What is the circuit symbol for a thermistor?

Answer 3

Question 4

What is the circuit symbol for a variable resistor?

Answer 4

Question 5

What is the circuit symbol for a light dependent resistor?

Answer 5

Question 6

What is electric current?

Answer 6

The rate of flow of electrical charge.
In metal wires this charge is carried by electrons.

Question 7

How is current measured?

Answer 7

Through an ammeter connected in series with the component.

Question 8

What must a circuit be for an electrical charge to flow?

Answer 8

A closed circuit.

Question 9

What is a coulomb?

Answer 9

The charge that passes a point in a circuit when there is a current of one ampere for one second.

Question 10

What is resistance?

Answer 10

A measure of how hard it is for charge to flow through a component or a material.

Question 11

Explain why the resistance in a wire changes as the wire gets hotter.

Answer 11

As the wire gets hotter the atomic vibrations are larger so electrons collide with atoms more frequently and the resistance increases.

Question 12

Required Practical 15: Investigating resistance

Answer 12

• Set up a circuit to measure the potential difference and current for a wire at different lengths along the wire
• Calculate the resistance using R = V / I
• Plot a graph : Resistance is directly proportional to length
  _Sources of error_:
• Heating effect of the wire - use a low potential difference and only turn current on briefly and allow it to cool between readings
• Measuring the length between the crocodile clips consistently

Question 13

What are Ohmic conductors?

Answer 13

At a constant temperature, the resistance stays constant when the current changes.

Question 14

What is the graph for a filament lamp?

Answer 14

Non-ohmic

Question 15

What is the graph for a diode?

Answer 15

Non-ohmic

Question 16

What is the basic circuit for measuring the resistance of a component?

Answer 16

Question 17

What is the graph for a thermistor?

Answer 17

Question 18

What is a thermistor used for?

Answer 18

Temperature sensors in fire alarm systems.
Thermostats fur switching on devices at certain temperatures.

Question 19

What is the graph of an LDR?

Answer 19

Question 20

What are LDRs used for?

Answer 20

Security and street lamps.

Question 21

Required Practical 16: Investing I-V characteristics of components

Answer 21

• Set up the circuit for each component
• Adjust the variable resistor and record sever pairs of ammeter and voltmeter readings in a table

Question 22

Compare potential difference, current and resistance in a series and parallel circuit.

Answer 22

Series:
- Potential difference is shared: V_cell = V₁ + V₂
- Current is same through each lamp: I₁ = I₂
- Total resistance is is the sum of the resistance of each lamp
Parallel:
- Potential difference across each lamp is the same: V_cell = V₁ = V₂
- Total current is the sum of the current through each lamp: I_total = I₁ + I₂
- The total resistance is less than the resistance of the component with the smallest resistance in the circuit

Question 23

What is a direct current?

Answer 23

The electrons move from the negative terminal to the positive terminal and the current is always in the same direction.

Question 24

What is an alternating current?

Answer 24

The direction of the movement of the electrons is constantly changing. This means the potential difference is also constantly changing.

Question 25

What is the pd-time graph for dc?

Answer 25

Question 26

What is the pd-time graph for ac?

Answer 26

Question 27

Describe the energy supply of the UK.

Answer 27

Frequency of 50 Hz and pd of 230 V

Question 28

What devices use a dc supply?

Answer 28

Mobile phone, electric toothbrush, remote control, hand held vacuum cleaner.
Devices that use a battery or cell, not the mains supply.

Question 29

What is the colour, potential difference with the Earth and purpose of the Earth wire?

Answer 29

Green and yellow stripes
0 V
Safety wire, only carries a current if there is a fault

Question 30

What is the colour, potential difference with the Earth and purpose of the Live wire?

Answer 30

Brown
230 V
Carries the alternating current from the supply, connects to a fuse.

Question 31

What is the colour, potential difference with the Earth and purpose of the Neutral wire?

Answer 31

Blue
Around 0 V
Completes the circuit.

Question 32

What dues the fuse contain?

Answer 32

A wire that will melt if the current gets too high.

Question 33

What happens if a person touches a live wire?

Answer 33

The current travels through them to the ground and they get an electric shock.

Question 34

What is the Earth wire?

Answer 34

A safety wire to stop the actual appliance becoming live if the live wire touches a conducting part of the appliance.

Question 35

What are two dangers of using the mains supply?

Answer 35

Electric shock from contact with a live connection
Fire caused by too much current

Question 36

Why is different coloured insulation used in a three-core cable?

Answer 36

To identify the different wires, to connect wires correctly for safety and for the appliance to work.

Question 37

Draw what a three-core cable looks like.

Answer 37

Question 38

An electrical appliance transfers more energy if it:

Answer 38

• Has a higher power rating
• Is switched on for more time

Question 39

What is the difference between dc and ac in terms of where they transfer energy from?

Answer 39

Dc supply transfer from cells and batteries whilst an ac supply transfers from the mains.

Question 40

What is electrical work?

Answer 40

How energy is transferred when charge flows in a circuit.

Question 41

Give an example of a device that transfers energy by:
a). Kinetic energy
b). Thermal energy

Answer 41

a). Any electrical device with a spinning motor e.g. washing machine
b). Any electrical device designed to get hot e.g. Hairdryer

Question 42

What is the National Grid?

Answer 42

The system of cables and transformers in the UK that links power stations to consumers.

Question 43

What are step-up transformers used for?

Answer 43

To increase the potential difference from the power stations.

Question 44

What are step-down transformers used for?

Answer 44

To decrease the pd from the transmission cables so it’s much lower for use in homes.

Question 45

Why is the National Grid system an efficient way to transfer energy?

Answer 45

A step up transformer steps up the pd and reduces the current so reducing the current reduces the energy dissipated by the current heating effect. In addition, wires with low resistance are also used to help minimise the energy dissipated.