Physics: Danger of Electricity, EMF

Question 1

Frayed Wiring

Answer 1

strands of wire with a higher resistance at one point. A heating effect may be enough to melt the insulation and cause a fire.

Question 2

Extension leads

Answer 2

may overheat if used when coiled up. The current flowing will warm the wire, but the tight bundle means that the heat has less room to escape.

Question 3

water leaks into a plug/socket

Answer 3

risk of someone getting electrocuted as water will conduct the current.

Question 4

lawnmower of electric hedgetrimmer

Answer 4

danger of cutting through the cable. A plug-in RCD should always be used to avoid electrocution.

Question 5

Earth wire (yellow and green)

Answer 5

Stops metal appliances becoming live if there is a fault.

Question 6

Live wire (brown)

Answer 6

prevents electric shocks from occurring if the appliance malfunctions or the live
wire breaks off and touches the case of the plug

Question 7

Fuse

Answer 7

always connected to the live wire. If the current gets too high the fuse will ‘blow’ and break the circuit.

Question 8

Neutral wire

Answer 8

blue

Question 9

Voltages as low

Answer 9

as 50V cause serious risk of electrocution

Question 10

Protecting device/user

Answer 10

double insulation
earthing
fuses
circuit breakers

Question 11

double insulated,

Answer 11

Insulation around the wires themselves
A non-metallic case that acts as a second layer of insulation

Question 12

Earthing

Answer 12

The earth wire provides alow resistance path to the earth
It causes asurge of current in the earth wireand hence also in the live wire
The high current through the fuse causes it tomelt and break
This cuts off the supply of electricity to the appliance, making it safe

Question 13

Fuses

Answer 13

Fuses usually consist of a glass cylinder containing a thin metalwire
The wireheats upandmelts
This causes the wire tobreak, breaking thecircuitandstoppingthecurrent
Fuses come in values of3 A,5 Aand13 A

Question 14

Trip switches

Answer 14

When the current is too high the switch trips; (automatically flicks to the off
position)
This stops the current flowing in that circuit

Question 15

Induced e.m.f.

Answer 15

whenever there isrelative
movementbetween the conductor and a magnetic field
the conductor moves in a stationary magnetic field
the conductor is stationary in a changing magnetic field

Question 16

Induced e.m.f. due to a moving conductor

Answer 16

electrical conductor moving in a fixed magnetic field
the conductor (e.g. a wire)cutsthe field lines
an e.m.f. isinducedin the wire

Question 17

Induced emf can be increased by

Answer 17

moving wire faster, using stronger magnet, looping wire multiple times through the field

Question 18

Reverse the emf & current by

Answer 18

moving wire in opposite direction and turning magnet around