physics qma revision 2018

Question 1

how to convert milliamps to amps

Answer 1

/ 1000

Question 2

how to convert megavolts to volts

Answer 2

x1,000,000

Question 3

function of ammeter

Answer 3

measures current

Question 4

function of voltmeter

Answer 4

measures potential difference (voltage)

Question 5

function of fixed resistor

Answer 5

allows a specific amount of current and voltage through

Question 6

function of thermistor

Answer 6

as the temperature changes, the resistance changes

Question 7

function of diode

Answer 7

only allows current to flow in one direction

Question 8

function of light dependant resistor

Answer 8

as the light changes the resistance changes

Question 9

what does resistance do

Answer 9

slows the flow of electrons in the circuit

Question 10

what does high resistance mean

Answer 10

low current
low energy
higher potentail difference

Question 11

what is ohms law

Answer 11

current is directly proportional to potential difference as long as the temperature is constant

Question 12

what is a component that obeys ohms law called

Answer 12

an ohmic conductor

Question 13

what is a series circuit

Answer 13

current is the same around the circuit
voltage splits but adds up what you put in
resistance gets added together

Question 14

what is a parallel circuit

Answer 14

voltage is the same around the circuit
current splits but adds up what you put in
resistance is smaller than your lowest resistor

Question 15

what happens as you increase the temperature on a thermistor

Answer 15

decrease the resistance

Question 16

what happens as you increase the light on an ldr

Answer 16

descrease the resistance

Question 17

how to calculate kinetic energy

Answer 17

0.5 x mass x speed^2

Question 18

how to calculate gravitatinoal potential energy

Answer 18

mass x gravitational field strength x height

Question 19

how to calculate power

Answer 19

energy transfered / time
work done / time
potential difference * current
current^2 x resistance

Question 20

how to calculate efficiency

Answer 20

useful output energy transfer / total input energy transfer

useful power output / total power output

Question 21

how to calculate charge flow

Answer 21

current * time

Question 22

how to calculate potential difference

Answer 22

current * resistance

Question 23

how to calculate energy transferred

Answer 23

power x time

charge flow x potential difference

Question 24

method to calculate resistance for a filament bulb

Answer 24

• measure potential difference with a voltmeter
• calculate resistance using V / I
• independent variable (x axis) = potential difference
• dependent variable (y axis) = current

Question 25

is a filament lamp an ohmic conductor

Answer 25

no

Question 26

why isn't a filament lamp an ohmic conductor

Answer 26

the graph curves because the electrons gain kinetic energy and collide with vibrating ions more frequently, causing resistance and thermal energy being given off

Question 27

are fixed resistors ohmic conductors

Answer 27

yes

Question 28

how does steepness on an IV graph correspond with resistance

Answer 28

the steeper the gradient, the higher the resistance

Question 29

what is the independent variable in the length of the wire experiment

Answer 29

length of wire (x axst)

Question 30

what is the dependent variable in the length of the wire experiment

Answer 30

resistance (y axis)

Question 31

what is power measured in?

Answer 31

watts

Question 32

what colour is the earth wire and what is its function

Answer 32

yellow and green, prevents shocks and fires, 0v unless there is a problem

Question 33

what colour is the neutral wire and what is its function

Answer 33

blue, at or close to 0v

Question 34

what colour is the live wire and what is its function

Answer 34

AC, alternates between high positive and high negative voltage (230v)

Question 35

why are wires and pins made of metal

Answer 35

they have delocalised (sea of free electrons)

Question 36

why are plug case and outer insulations made of plastic

Answer 36

they do not conduct electricity

Question 37

what do transformers do

Answer 37

change the potential difference

Question 38

what do step up transformers do and why

Answer 38

increase the potential difference and decrease the current so its more efficient (less thermal energy is wasted from resistance in wire)

Question 39

what do step down transformers do and why

Answer 39

decrease the voltage and increase the current so the voltage is at 230V, safe for home levels

Question 40

what is power

Answer 40

the rate at which work is done

Question 41

what is work done

Answer 41

energy transferred

Question 42

what is current

Answer 42

the rate of flow of electron (charge) around a circuit

Question 43

what happens when two insulating materials are rubbed together

Answer 43

electrons only move, this means a material with more electrons than protons has a negative charge and the one with more protons has an equal but opposite positive charge

Question 44

what happens when a rod is rubbed on a polythene cloth

Answer 44

the rod becomes negative because it gains more electrons, the cloth becomes positive and has an equal and opposite charge to the rod

Question 45

what happens when a rod is rubbed on an acetate cloth

Answer 45

the rod becomes positive because it loses electrons so it has more protons than electrons, the cloth becomes negative and has an equal and opposite charge to the rod

Question 46

what is a danger of static electricity

Answer 46

sparks causing fuel to ignite e.g. in cars and planes

Question 47

how to earth a plane for refuelling

Answer 47

attach a metal cable, negative electrons will flow through. the charge will go from the plane to the ground and the charge will not build up instead it will be destroyed

Question 48

in electrical fields which way do the arrows flow

Answer 48

from positive to negative

Question 49

in electrical fields how can you increase the repulsion

Answer 49

by decreasing the distance

Question 50

in a comb and moving belt model how is the belt charged and why

Answer 50

the belt is positively charged because the belt loses negative electrons to the dome

Question 51

what happens when you touch the dome

Answer 51

your hair sticks up because of the negative charge