electricity

Question 1

what is current

Answer 1

the rate of flow of charge

Question 2

what is electric current in a solid metallic conductor

Answer 2

the flow of negatively charged electrons

Question 3

when does current split (in series or in parallel )

Answer 3

in parallel circuits, the current splits between the 2 branches (in series it is the same)

Question 4

when does voltage split (in series or in parallel )

Answer 4

in series circuits, the voltage splits between the components (in parallel the voltage across 2 components is equal)

Question 5

how does current vary with voltage in wires

Answer 5

current is directly proportional to voltage in wires (obeys Ohm’s law)

Question 6

how does current vary with voltage in resistors

Answer 6

current is proportional to voltage in resistors

Question 7

how does current vary with voltage in a filament lamp

Answer 7

NOT proportional.
curved line when you plot I and V
as temperature increases so does resistance

Question 8

how does current vary with voltage in a diode

Answer 8

NOT proportional

flat line then suddenly peaks: current only flows through a diode in one direction

Question 9

what is the effect of increasing resistance in a circuit on current

Answer 9

current decreases

Question 10

describe the variation in resistance with LDRs

Answer 10

in bright light, resistance falls

in darkness, resistance is highest

Question 11

describe the qualitative variation of resistors with thermistors

Answer 11

high temperature= low resistance

low lemperature= high resistance

Question 12

what can be used to detect the presence of current in a circuit

Answer 12

lamp or LED

Question 13

define voltage

Answer 13

the energy transferred per unit charge ( V = j/C)

Question 14

how does insulation/ double insulation protect us

Answer 14

the insulator (usually plastic) stops a current flowing, meaning you can’t get a shock

Question 15

how do earthing and fuses/ circuit breakers prevent fires and shocks

Answer 15

If a fault develops in which the live wire touches the metal casing, then the current flows through the casing and earth wire to the ground.
The surge in current causes the fuse to melt/the circuit breaker to trip, cutting off the live supply.

Question 16

why do resistors get hot when an electric current passes through them

Answer 16

1) when there is an electric current in a resistor, there is an energy transfer which heats up the resistor
2) the electons collide with the ions in the lattice that make up the resistor as they flow through it; this gives the ions energy which causes them to vibrate and heat up.
3) this heating effect means the resistance increases so more voltage is needed to produce the same current

Question 17

when is the heating effect used in domestic contexts

Answer 17

toasters

Question 18

advantages/ disadvantages of series circuits

Answer 18

series advantage – fewer wires;
series advantage – lower resistance values;
series disadvantage – one fails, circuit fails;
series disadvantage – no independent control;

Question 19

Which fuse should you use with an appliance that takes s current of 5 A

Answer 19

Closest above that, eg 5.5 A

Question 20

what is voltage (informal)

Answer 20

what drives the current round ( a bit like “electrical pressure”) unit V (volts)

Question 21

what is resistance

Answer 21

anything that slows the current down unit ohm

Question 22

battery supply and mains supply: d.c or a.c

Answer 22

battery = d.c 
mains = a.c (in uk it is 230 v)

Question 23

resistance current and voltage formula

Answer 23

V= IR

Question 24

charge formula

Answer 24

charge = currrent x time

Q=IT

Question 25

energy transferred formulas

Answer 25

E= Q V
( E= QIR)
( E= IVT)