Electricity

Question 1

The equation for charge Q =

Answer 1

Q = IT

Question 2

Current is the ….

Answer 2

flow of charge per second

Question 3

What is an electrical conductor and give examples?

Answer 3

a material that current flows well in
eg metals, graphite (as they have delocalised electrons)

Question 4

What is an electrical insulator and give examples?

Answer 4

a material that current does not flow well in
eg plastic, rubber,

Question 5

Describe what happens when we charge by friction.

Answer 5

eg polythene rubbed with cloth
rub cloth on polythene
electrons gain energy and move from cloth to rod
rod becomes negatively charged
cloth becomes positively charged

Question 6

Why can we only charge insulators and not conductors?

Answer 6

Conductors cannot be charged as they can conduct so would carry the charge away

Question 7

Laws of electrostatic forces?

Answer 7

Like charges repel
Unlike charges attract

Question 8

Dangers of electrostatics?

Answer 8

Refueling aircraft and tankers
Charge can build up and all jump at once in the form of a spark. This can ignite the fuel causing a fire.
Earthing metal stops charge building up.

Question 9

Uses of electrostatics?

Answer 9

Photocopiers
Inkjet printers
Paper is charged with one charge and the ink charged with the opposite charge.
Unlike charges attract so ink is attracted to the paper

Smoke precipitators
charge smoke particles in chimney
charge plates each side with opposite charge
unlike charges attract so smoke sticks to plates and is removed before the gas enter the air

Question 10

Equation for current I

Answer 10

I = Q/t

Q= It

Question 11

Equation for voltage

Answer 11

Voltage = energy/ charge
V = E/Q
= joules per coulomb

Question 12

Equation for resistance

Answer 12

V = IR

Question 13

Current in series is……

Answer 13

The same everywhere

Question 14

Voltage in series….

Answer 14

Voltage splits

Bigger resistance takes bigger voltage

Question 15

Current in parallel…..

Answer 15

Splits at junctions between branches.
Larger resistance takes smaller current

Question 16

Voltage in parallel…..

Answer 16

Same across each branch

Question 17

Power =

Answer 17

Power = IV

Question 18

Power lost to heat in a circuit =

Answer 18

P = IxIxR

Question 19

List 4 things that protect a device or user in electrical circuits.

Answer 19

Double insulation
Earthing
Fuses
Circuit breakers

Question 20

Energy transferred =

Answer 20

Energy transferred = IVt

Question 21

What’s the difference between ac and dc current?

Answer 21

AC is alternating - changes direction 50 times per second
DC is direct and flows in one direction only

AC in mains
DC in batteries

Question 22

For wires and resistors, as temperature increases then resistance ….

Answer 22

Increases
Particles have more KE so electrons collide more with the lattice ions

Question 23

Conventional current flows positive to negative but in a metal conductor electrons in the wire flow…

Answer 23

Negative to positive

Question 24

What can we use in a circuit to indicate the presence of current?

Answer 24

an LED

Question 25

What resistance does an LDR have in the light?

Answer 25

light gives low Resistance

Question 26

What resistance does a thermistor have when hot?

Answer 26

hot gives low Resistance

Question 27

Are series or parallel circuits best for domestic lighting? Why?

Answer 27

parallel
each light can be controlled separately by own switch
if one buld blows, others still work

Question 28

Why are some Christams lights wired in series?

Answer 28

less wires
cheaper
voltage shared between bulbs