Electricity

Question 1

what is current

Answer 1

current is the rate of flow of charge. It is measured in Amps (A)

Question 2

What is voltage (potential difference)

Answer 2

Voltage is the driving force that pushes the charge around.

Question 3

What is resistance

Answer 3

Resistance is anything in the circuit which slows the flow down. Measured in Ohms

Question 4

What is the operation of a Variable resistor

Answer 4

Variable resistors allow you to adjust the value of voltage by changing the current flowing into a component with resistance.

Question 5

What is the operation of a diode

Answer 5

It acts as a one way switch that allows current to flow in one direction but restricts it from flowing the other with high resistance.

Question 6

what happens when electrons bump into atoms

Answer 6

it can cause heat due to resistance. it can cause wires to get hotter

Question 7

how to calculate current

Answer 7

Current = Charge
——————-
Time

Question 8

how to calculate voltage

Answer 8

Voltage = Energy (work done)
————–
Charge

Question 9

How to calculate resistance

Answer 9

Resistance = Voltage
————-
Current

Question 10

How to measure current in a circuit

Answer 10

Question 11

Ohms law

Answer 11

Ohm’s law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperature remain constant.

Question 12

What might effect resistance

Answer 12

• Current,
• length of wire: more wire=more resistance
• material of wire, some are better conductors
• temp, higher temp = lower resistance
• thickness, thinner wires conduct easier
• parallel or series, parrallel= lower resistance and series= sum of all resistors

Question 13

Resistance in a filament lamp

Answer 13

• current increases so temp of lamp increases
• the lamp is metal, so the raised temp causes an increased resistance
• resistance opposes the current, causing the current to increase at a slower rate

Question 14

Metal resistor IV graph

Answer 14

Has a constant gradient, so a constant resistance. This is because the current is directly proportional to potential difference

Question 15

Bulb IV graph

Answer 15

has decreasing gradient, so an increasing resistance. This is because the wire gets hot.

Question 16

Diode IV graph

Answer 16

has a low gradient (high resistance) until the threshold current.

Question 17

What is a LDR

Answer 17

a resistor that is dependent on the intensity of light. If there is an increase of light, there is a decrease of resistance. Used often for automatic night lights, burgled alarms, outdoor lighting.

Question 18

what is a thermistor

Answer 18

Temperature dependent resistor. If temp is increased resistance decreases. They’re used for car engines, thermostats and temp detectors

Question 19

Current in a series circuit

Answer 19

Current is the same in any part of the circuit, this is because a series circuit is one loop; all electrons in that loop form one current

Question 20

voltage in a series circuit

Answer 20

the potential difference supplied is equal to the total of the potential differences across all other components

Question 21

Resistance in a series circuit

Answer 21

electrons have to pass through all resistors, so total resistance is sum of resistors.

Rtotal= R (1) + R(2) + R(3) +…

Question 22

Current in a Parallel Circuit

Answer 22

The overall current is shared between the loops

Question 23

Voltage in a Parallel circuit

Answer 23

the voltage is the same for each loop

Question 24

Resistance in a Parallel circuit

Answer 24

electrons have a choice of path so overall resistance = lower because the effective resistance is adding the reciprocals of the individual resistors

Question 25

filament lamp IV graph

Answer 25

Question 26

what does the amount of current flowing through a circuit depend on

Answer 26

Potential difference and resistance

Question 27

What two equations do you use to find power (watts)

Answer 27

Power = Voltage x current or Power = energy / time

Question 28

What does a switch do

Answer 28

A switch used to turn a circuit on (closed) and off (open).

Question 29

What does a lamp do

Answer 29

An electrical current heats the filament in a bulb so that it gives out light.

Question 30

What does a fixed resistor do

Answer 30

A resistor restricts or limits the flow of electrical current. A fixed resistor has a resistance that does not change.

Question 31

What is charge

Answer 31

Charge is a property of a body which experiences a force in an electric field. Charge is measured in coulombs (C). There is more charge when there is more current.

Question 32

Equation for charge

Answer 32

charge = current × time

Question 33

What is direct current

Answer 33

- flows in one direction - On a voltage-time graph this would appear as a straight horizontal line at a constant voltage - Car batteries, dry cells and solar cells all provide a direct current (dc) that only flows in one direction.

Question 34

What is alternating current

Answer 34

-An alternating current regularly changes direction. -alternating between positive and negative voltages on a voltage time graph - used in the mains electric supply

Question 35

Label the diagram

Answer 35

Question 36

What do you use an Ammeter for

Answer 36

Measuring current (in amps). It must always be in a series

Question 37

What does a voltmeter measure

Answer 37

Potential difference (volts), ALWAYS in parallel around whatever you are testing, not around any other bit

Question 38

What type of components have a straight line on an IV graph

Answer 38

Linear components (resistor or Ohmic conductor)

Question 39

What type of components have a curved line on an IV Graph

Answer 39

Non linear components ( filament lamp or a diode)

Question 40

How is alternating current produced

Answer 40

By alternating potential difference in which positive and negative ends keep alternating

Question 41

How is DC produced

Answer 41

Direct potential difference.

Question 42

How are electrical appliances connected to mains supply

Answer 42

3 core cables, they have a core of copper, coloured plastic coating

Question 43

What is the Neutral wire for

Answer 43

- it completes the circuit - Current flows through it - It is blue

Question 44

What is the live wire for

Answer 44

- provides the alternating provides the alternating potential difference from the mains supply - it is brown

Question 45

What is the earth wire for

Answer 45

- protecting the wiring and safety - stops appliance casing from becoming live. - doesn’t carry current - Green and yellow

Question 46

What is a use for static charge and a danger

Answer 46

- diffibrulators -explosions

Question 47

How might touching the live wire give you a shock

Answer 47

- large potential difference is produced across your body, current flows thru you - causing an electric shock - because your body provides a link for the current to flow thru you between the supply and the earth - this can happen even if the plug socket is turned off = due to pd in live wire

Question 48

What is the National grid

Answer 48

- system of cables and transformers, - connects power stations to consumers across the UK

Question 49

When does demand increase for electricity

Answer 49

- people get up in morning - return home from work/school - when it gets dark or cold - popular events on TV

Question 50

What output do power stations run at

Answer 50

- maximum output - so there’s spare capacity to cope with high demand

Question 51

What is the voltage in the national grid

Answer 51

400 000 V

Question 52

How does the step up transformers work

Answer 52

- step up the potential difference at one end: for efficient transmission - step down for safe, unstable levels at the other end