2: ELECTRICITY

Question 1

what side is the plus sign on on a cell symbol

Answer 1

the left side

Question 2

the process of electrons in a circuit (4)

Answer 2

1 electrons have charge
2 charge carry energy through the wire from the cell to the bulb where all the energy is converted into light
3 the charge then returns to the cell to gain more energy
4 this is a continuous process

Question 3

from where to where does current travel

Answer 3

from positive to negative (nonsense but oh well)

Question 4

what relationship do pd and current have in an ohmic conductor (fixed resistor)

Answer 4

directly proportional

Question 5

why are metals non ohmic

Answer 5

bc they have a change in resistance if you increase the pd and current

Question 6

filament bulb graphs (3)

Answer 6

1. resistance is NOT constant
2. this is due to delocalised electrons colliding with an ionic lattice, causing them to vibrate more and resulting in a temp increase
3. this makes it harder for electrons to flow, so higher current is higher resistance

Question 7

what would happen to a resistor if the temperature increased

Answer 7

the resistance would increase (nonsense but the mark scheme)

Question 8

talk abt diodes

Answer 8

only let current flow in one direction, low resistance forward, high resistance backward

Question 9

resistance practical (2)

Answer 9

1. measure v and i on a metal wire with crocodile clips and calculate resistance
2. plot the graph, should end up with straight line

Question 10

series vs parallel circuits

Answer 10

series: total pd is shared across components
current is the same
total resistance is shared across components
vs
parallel: pd of each branch is pd of cell/battery
current is shared between branches
adding more resistors in parallel reduces total R as there is another path for current to travel

Question 11

talk abt thermistors (4)

Answer 11

1. if temp increases, resistance decreases
2. thermistor voltage supply decreases
3. bottom resistor gets bigger share of voltage
4. voltmeter reading increases, can be used to turn off heating

Question 12

talk abt LDRs (3)

Answer 12

1. if light intensity decreases, resistance increases
2. LDR gets bigger share of voltage
3. voltmeter reading increases, can turn on a street lamp for example

Question 13

talk abt mains electricity

Answer 13

AC, resulting from an alternating PD (freq of 50 Hz, voltage of 230V)

Question 14

talk abt the different wires

Answer 14

neutral wire: blue, stays at 0V
live wire: brown, switches between positive and negative pds of 230
earth wire: green and yellow, a safety feature, acts as an escape route for currents that could cause a shock if the appliance was touched. not needed if double insulation

Question 15

what is a fuse and what does it do

Answer 15

a thin metal wire in a tube designed to “melt” or “blow” if there is too high a current, disrupting the circuit
3A, 5A, 13A

Question 16

talk abt the national grid (4)

Answer 16

1. power stations produce too high currents
2. if this went straight to the grid, a lot of power would be lost as heat from the resistance of the cables
3. a step up transformer increases the voltage (132kV) which decreases the current, reducing the power lost to heating
4. a step down transformer decreases the voltage to a safer and usable 230V for homes

Question 17

what is static electricity

Answer 17

when electrons are transferred between insulating materials, leaving one positively and one negatively charged, they stay charged

Question 18

arrows for positive vs negative charges on a field graph

Answer 18

positive = going away
negative = going towards

Question 18

talk abt a van de graaff

Answer 18

every part of you becomes positively charged, your hair will repel from your head bc like charges repel

Question 19

how do we know the field gets weaker

Answer 19

the lines begin to diverge from the charged object