Electricity

Question 1

What is a fuse?

Answer 1

a safety device which melts to break the circuit if the electrical current flowing through it exceeds a specified value

Question 2

what is a thermistor?

Answer 2

an electrical device whose resistance decreases as the temperature increases

Question 3

what is current?

Answer 3

a flow of electric charge

Question 4

the greater the rate of flow….

Answer 4

the higher the current

Question 5

equation for charge , current and time

Answer 5

charge (Columbus) = current (amperes) x time (seconds) Q=IT

Question 6

potential difference

Answer 6

the force that pushes the charge round

Question 7

resistance

Answer 7

anything that slows flow down

Question 8

the greater the resistance across a component ………….

Answer 8

the smaller the current that flows

The more difficult it is for the charge to flow

Question 9

two factors that current depends on

Answer 9

1) potential difference 2) resistance

Question 10

the bigger the potential difference across a component …

Answer 10

the greater the flow of charge through the component the bigger the current

Question 11

Equation for potential difference

Answer 11

current x resistance V= IR

Question 12

What’s an ohmic conductor?

Answer 12

a device that obeys ohms law

Question 13

What’s Ohm’s Law?

Answer 13

V=IR

Question 14

What are I-V characteristics?

Answer 14

Graphs which show how the Current changes with Voltage in a components

Question 15

shallow gradient in a I-V graph means

Answer 15

high resistance -large potential difference needed to produce a small amount

Question 16

what does it mean when a straight line cuts through the origin

Answer 16

that the current and voltage are directly proportional

Question 17

steep gradient in a I-V graph means

Answer 17

low resistance - large current will flow though a small voltage (large voltage not needed)

Question 18

list four components for which the resistance is not constant due to the current changing

Answer 18

1) lamps 2) diodes 3)thermistor 4) LDR (light dependant resistor)

Question 19

filament lamps

Answer 19

As the current through a filament lamp increases, its temperature increase. This causes the resistance to increase as the current increases. It is indicated by a curved graph.

Question 20

Diodes

describe its graph as well

Answer 20

current flows through only one direction high resistance if current is reversed

Question 21

LDR

Answer 21

dependant on light intensity

bright = resistance falls

darkness = resistance increases

Question 22

What is a variable resistor?

Answer 22

a resistor where the vaue of the resistance can be changed

Question 23

what is a light emitting diode?

Answer 23

only allows current to flow in the forward direction and emits light when current flows through them

Question 24

What is the rule for voltage, current and resistance in series circuits?

Answer 24

voltage is shared

V_total = V₁ + V₂ + ……….

Current is the same everywhere

I = V/R

Resistance adds up

R_total = R₁ + R₂ + ……….

Question 25

how must voltmeters and ammeters be connected

Answer 25

ammeters should always be connected in series voltmeters should always be connected in parallel

Question 26

What is the rule for voltage, current and resistance in **parallel circuits**?

Answer 26

Voltage is the same across all components current is shared between branches Adding a resistor reduces the total resistance

Question 27

why does adding resistors in parallel reduces the total resistance?

Answer 27

Because, in parallel, there are more paths for the current to take, allowing it to flow more easily

Question 28

the equation for power in a circuit?

Answer 28

P = voltage x current p = current ² x resistance

Question 29

What is a direct current supply?

Answer 29

current that flows in one direction - has a potential difference that is always positive or negative - the type of current that is supplied by batteries and cells

Question 30

What is an alternating current supply?

Answer 30

- the current is always changing direction - has a potential difference that alternates from positive to negative - used in mains electricity

Question 31

What is the UK mains electricity and how many times does it change directions per second?

Answer 31

230V changes direction 50 times per second therefore it has 50Hz

Question 32

the 3 different wires in a three-core cable are:

Answer 32

- **live wire** (brown) - **neutral wire** (blue) - **earth wire** (green and yellow stripes)

Question 33

What does the live wire do?

Answer 33

- provides the alternating current (at about 230V) from the mains supply -

Question 34

What does the neutral (blue) wire?

Answer 34

- completes the circuit and carriers away current - it is around 0V

Question 35

What does Earth Wire do?

Answer 35

- for protecting the wiring and for safety - stops the appliance casing from becoming live - The earth wire is at 0 V, it only carries a current if there is a fault.

Question 36

What happens inside a three-core cable during operation?

Answer 36

- the potential difference causes current to flow through the live and the neutral wires - the live wire carries the alternating potential from the supply - the neutral wire completes the circuit - current will only flow in the earth wire if there is a fault connecting it to a non-zero potential

Question 37

A live wire can be dangerous even if a switch in the circuit is open because.....

Answer 37

there's still an alternating current and all it needs is a path for the electricity to flow through

Question 38

Whenever charge flow, it has to overcome the resistance of the circuit. This requires energy, therefore:

Answer 38

- work is done when charge flows - the amount of work done depends on the amount of charge that flows and the potential difference

Question 39

What are the two equations for energy transfer?

Answer 39

E = power x time E = charge flow x potential difference