Topic 2: Electricity

Question 1

what is the voltage in a series circuit?

Answer 1

shared amongst components
V(total) = V(1) + V(2) + V(3)

Question 2

what is the current in a series circuit?

Answer 2

the current is constant in all parts
I(1) = I(2) = I(3)

Question 3

what is the resistance in a series circuit?

Answer 3

the resistance is the sum of the individual resistances of components
R(total) = R(1) + R(2) + R(3)

Question 4

what is the voltage in parallel circuits?

Answer 4

all components get the full voltage
V(total) = V(1) + V(2) + V(3)

Question 5

what is the current in a parallel circuit?

Answer 5

the current is split between branches based on resistance
I(total) = I(1) + I(2) + I(3)

Question 6

what is the resistance in parallel circuits?

Answer 6

reciprocal of total resistance is the sum of the reciprocals of the individual resistances

Question 7

how to investigate the current in resistor at constant temperature varied with the potential difference across the resistor

Answer 7

• measure the current using an ammeter
• measure the potential difference using a voltmeter
• vary the resistance of the variable resistor
• record a range of values of current and potential difference
• ensure the current is low to avoid temperature increase
• reverse connect of R to power supply
• repeat measurements of I and V in negative direction
• plot a graph of current against potential difference

Question 8

in light dependant resistors (LDR) describe the resistance when it is light and dark

Answer 8

• when it is dark - resistance is high
• when it is light - resistance is low

Question 9

describe what happens in light dependant resistors (LDR) in a circuit when it is dark

Answer 9

• when it’s dark
• high resistance
• low current (stops the current from flowing in)
• so a high potential difference is needed to push the current through

Question 10

describe what happens in light dependant resistors (LDR) in a circuit when it is light

Answer 10

• when it is light
• low resistance
• high current
• low potential difference
• light bulb will turn off

Question 11

what is a thermistor dependant on?

Answer 11

temperature - so would be connected to a fan or a boiler

Question 12

describe the resistance when it is cold and when it hot in a thermistor

Answer 12

• when it is cold you will get high resistance
• when it is hot you will get low resistance

Question 13

describe what happens in a thermistor in a circuit when it is cold

Answer 13

• when it is cold
• high resistance
• low current
• high potential difference

Question 14

describe what happens in a thermistor in a circuit when it is hot

Answer 14

• low resistance
• high current
• low potential difference
• will cause the fan to turn on

Question 15

describe the current in a series circuit and a parallel circuit

Answer 15

series - current is the same everywhere

parallel - current is shared between components

Question 16

describe the potential difference in a series circuit and a parallel circuit

Answer 16

series - potential difference is shared between components

parallel - potential difference is the same everywhere

Question 17

describe the resistance in a series circuit and a parallel circuit

Answer 17

series - total resistance = R1 + R2
(adds up)

parallel - resistance is lower than the lowest resistance

Question 18

what’s an insulator?

Answer 18

does not allow electrical charge to flow - plastics/ rubber

Question 19

what is a conductor?

Answer 19

allow the flow of charge through the material - metals - delocalised electrons

Question 20

how to build static charge?

Answer 20

• two insulating materials
• rub the two insulating materials against each other
• this will cause a transfer of electrons
• if the potential difference is large enough - you will get a spark - flow of electrons

Question 21

positive electric field

Answer 21

• it points outwards

Question 22

negative electric field

Answer 22

• points inwards

Question 23

what is the national grid made up of?

Answer 23

step-up transformer
cables/ pylon
step-down transformer

Question 24

what does the step-up transformer do?

Answer 24

• increases pd
• decreased current
• less resistance
• reduces energy lost as heat

Question 25

what do the cables/ pylons do?

Answer 25

carry electrical charge and distribute electricity across the country

Question 26

what does the step-down transformer do?

Answer 26

- decreases pd - increases current - makes it safe to use homes and businesses

Question 27

change of state from solid to liquid

Answer 27

melting

Question 28

change of state from liquid to gas

Answer 28

vaporisation, evaporation

Question 29

change of state from solid to gas

Answer 29

sublimation

Question 30

how to know there’s a change of state on a graph?

Answer 30

- flat part of the graph

Question 31

why does the temperature not increase when changing the state?

Answer 31

- temperature does not increase - energy is used to break bonds - separate particles

Question 32

increase in temperature

Answer 32

particles are gaining kinetic energy internal energy is increasing

Question 33

Describe what the live wire (brown) does

Answer 33

Provides an alternating potential difference (at about 230V) from the mains supply

Question 34

Describe what the neutral wire (blue) does

Answer 34

Neutral wire completes the circuit - when the appliance is operating normally, current flows through the live and neutral wires. (It's around 0V)

Question 35

Describe what the earth wire (green and yellow) does

Answer 35

- for protecting the wire and for safety - it stops the appliance casing from becoming live - it doesn't usually carry a current - only when there's a fault (It's also at 0V)

Question 36

Describe what happens to the resistance when temperature increases

Answer 36

The resistance increases

Question 37

What do we mean by the term conventional current?

Answer 37

Current flows from positive to negative side in a circuit

Question 38

Describe the graph for a ohmic conductor

Answer 38

- the current through the ohmic conductor (at constant temperature) - is directly proportional to potential difference, so you get a straight line

Question 39

Describe the graph for a Filament lamp

Answer 39

- as current increases, the temperature of the filament also increases - this means less current can flow per unit p.d. - so the graph gets shallower - hence the curve

Question 40

Describe the graph for a Diode

Answer 40

- current will only flow through a Diode in one direction - the Diode has very high resistance in the reverse direction

Question 41

Describe what happens when certain insulating materials are rubbed together

Answer 41

- when certain insulating materials are rubbed together - negatively charged electrons will be transferred from one material to another - this leaves the materials electrically charged