Electricity

Question 1

What happens in direct current

Answer 1

The flow of electrons are consistently in one direction around the circuit

Question 2

What happens in alternating current

Answer 2

The direction of electron flow continually reverses

Question 3

What is electrical current

Answer 3

A flow of electrons

Question 4

How do you measure current

Answer 4

With an ammeter that must be placed in series with that component

Question 5

How to measure p.d

Answer 5

With a voltmeter that must be placed in parallel with that component

Question 6

What do conductors and insulators have

Answer 6

• conductors has a low resistance

- insulators have a high resistance

Question 7

What is the iv characteristics for components

Answer 7

The relationship between current through and voltage across a component

Question 8

What is the voltage in a fixed resistor (resistor at a constant temp)

Answer 8

The voltage is directly proportional to the current

Question 9

What is ohms law

Answer 9

The rule that states that the current flowing through a resistor is directly proportional to the voltage across the resistor, provided the temp remains constant

Question 10

What does directly proportional mean

Answer 10

If one quantity goes up by a certain percentage/ number, the other quantity goes up by the same percentage/ quantity as well

Question 11

What would doubling the amount of energy into the resistor result in

Answer 11

A current twice as fast as the resistor

Question 12

How do you know if the relationship is ohms law

Answer 12

Because the resistance of the resistor is fixed (because the temp doesn’t change)

Question 13

What is a resistor…

Answer 13

An ohmic conductor

Question 14

What would a graph plotting p.d against current for a fixed resistor look like

Answer 14

Diagonal straight across (because it is directly proportional)

Question 15

What happens to the current in a filament bulb

Answer 15

• The current doesn’t increase at the same rate as the voltage
• doubling the amount of energy doesn’t cause a current twice as fast

Question 16

What happens if you put more energy into the bulb of a filament lamp

Answer 16

The harder it is for the current to flow (resistance of the bulb increases)

Question 17

What happens when the voltage increases in a filament lamp

Answer 17

The temp of the thin wires inside the bulb also increase

Question 18

What happens in result of the temp being increased in a filament bulb

Answer 18

• the increased vibrations of the ions in the filament make it harder for the electrons to get past

Question 19

What does a graph plotting p.d against current for a filament bulb look like

Answer 19

• Looks like an f

- The line is an upward curve that levels out and starts to dip as p.d increases

Question 20

What does a semiconductor diode do

Answer 20

Only allows current to flow in one direction

Question 21

What is the resistance of the diode like

Answer 21

Very large meaning no current would flow if the p.d was arranged to try and push current the wrong way

Question 22

What does a graph plotting p.d against diode look like

Answer 22

• line is horizontal on the x axis then curves upwards sharply

Question 23

What is the relationship in the resistance in a thermistor

Answer 23

• the resistance of a thermistor varies w temp

- when the temp increases the resistance decreases

Question 24

What is the relationship of the resistance of an LDR

Answer 24

• the resistance of an LDR varies with light intensity

- the more light on the LDR the smaller the resistance of it

Question 25

What happens in series circuits

Answer 25

Electrical components are connected one after another in a single loop

Question 26

What are the rules in a series circuit

Answer 26

- electrons with pass through every component on its way round the circuit - if one bulb is broken then the current won’t flow round - if one bulb goes out they all go out

Question 27

Current in series

Answer 27

- a series circuit is one loop | - all electrons in the loop form one current

Question 28

Explain how the resistance of a filament lamp changes as the p.d across it increases

Answer 28

- the pd increases which increases current flow - this heats wire - through heat, the current gains more energy causing it to vibrate more - this lets fewer electrons through and causes a greater resistance

Question 29

If light intensity decreases what happens to the pd and current

Answer 29

- pd increases | - current decreases

Question 30

What is pd

Answer 30

A measure of the energy given to the charge carries in a circuit

Question 31

What happens to pd in series circuits

Answer 31

- the pd difference supplied is equal to the total of the pd across other components

Question 32

Resistance in series

Answer 32

If resistors are connected in series, the current flows through both of them meaning the resistances are added together

Question 33

Key points in series circuits

Answer 33

- the current is the same through each component - the total pd difference of the power supply is shared between the components - the total resistance of the circuit is the sum of individual resistors

Question 34

What is the energy transferred each second equation

Answer 34

P = I x V or P = I squared R

Question 35

What do fuses do

Answer 35

- breaks the circuit if an appliance causes too much current to flow - this protects the wiring and the appliance if something goes wrong

Question 36

How does a fuse protect electrical circuits and appliances

Answer 36

- fuse contains a piece of wire that melts easily | - I’d current going through fuse is too great, wire heats up until it melts and breaks the circuit

Question 37

What are the standard fuse ratings

Answer 37

- 3A - 5A - 13A - if the device works at 3A, use a 5A fuse - if the device works at 10A, use a 13A fuse

Question 38

Why are copper wires used in a plug

Answer 38

They are good conductors

Question 39

Why is a plastic coating used in wires

Answer 39

Plastic is a good insulator

Question 40

What does the live wire do

Answer 40

Carries the current that enters the device

Question 41

What does the neutral wire do

Answer 41

0V, completely safe, connects to cable in wall and completes the circuit

Question 42

What does earth wire do

Answer 42

- if there is a fault, the earth wire carries away dangerous currents - low resistance path to ground

Question 43

What is the equation that links joules watts and power

Answer 43

E= p x t

Question 44

What does the national grid do

Answer 44

- It distributes electricity across the country | - the electricity is produced by a power station turning a generator

Question 45

What are transformers used for

Answer 45

- to change voltages and currents in transmission lines

Question 46

How do you determine whether the transformers will step up or down the voltage

Answer 46

The number of coils

Question 47

What does increasing voltage do in terms of transformers

Answer 47

Decreases current

Question 48

What does decreasing voltage do in terms of transformers

Answer 48

Increases current

Question 49

What does a step up transformer do and why

Answer 49

Increases voltage and reduces current | - less current so that less energy is lost through heating the wire

Question 50

What does a step down transformer do

Answer 50

Reduces the voltage to a safer voltage (230V) for home use

Question 51

What is the equation that links power current and resistance

Answer 51

P = I squared x R

Question 52

How to ensure minimum amount of power is lost from cables (national grid topic)

Answer 52

- they are thick so resistance is low | - high voltages used to reduce current through the transmission lines

Question 53

Advantages and disadvantages of transformers