Unit 3 - Electricity

Question 1

What do we use to measure currant

Answer 1

Ammeter

Question 2

Unit of measure for charge (Q)

Answer 2

Coulomb (C)

Question 3

Unit of measure for energy (w)

Answer 3

Joules (J)

Question 4

What do we use to measure resistance (Ω)

Answer 4

Ohms (Ω)

Question 5

Unit of measure for time (s)

Answer 5

Seconds (s)

Question 6

Unit of measure for voltage (V)

Answer 6

Volts (V)

Question 7

Unit of measure for power (P)

Answer 7

Watts (W)

Question 8

What are the hazards of electricity

Answer 8

Frayed cables (fire/electrocution), long cables (tripping), damaged plugs (fire/electrocution), water around sockets, pushing metal things into sockets (electrocution)

Question 9

What is insulation

Answer 9

Provides a protective layer around electric wires to prevent the conduction of electricity under the influence of an electric field

Question 10

What is double insulation

Answer 10

When the wire AND casing have a plastic cover. This stops the wire from touching the casing when the casing is an electrical conductor

Question 11

What is earthing

Answer 11

The 3rd wire is the earthing wire. It runs current into the ground to stop current circulating on the outside (causing shocks)

Question 12

What are circuit breakers

Answer 12

An electromagnetic switch that opens or trips when there is too much current (breaking the circuit but can be put back)

Question 13

What is a fuse

Answer 13

Fuses contain a thin wire that melts when a certain amount of current passes through it. This permanently brakes the circuit stopping a power over,lad

Question 14

Power =

Answer 14

P = I X V

Power (w) = current (A) X voltage (V)

Question 15

Energy transferred =

Answer 15

E = I X V X t

Energy transferred (J) = current (A) X voltage (V) X time (s)

Question 16

Voltage =

Answer 16

V = W / Q
Voltage (V) = energy (J) / charge (C)
OR
V = I X R
Voltage (V) = current (I) X resistance (Ω)

Question 17

Current =

Answer 17

I = Q/ S

Current (A) = charge (C) / time (s)

Question 18

Resistance =

Answer 18

Ω = V / I

Resistance (Ω) = voltage (V) / current (A)

Question 19

Properties of mains electricity

Answer 19

They are A.C (alternating current). This means that the voltage / current switches directions 50 cycles per second.
It’s always 230V in the UK

Question 20

Properties of direct current

Answer 20

Direct current (D.C) mains are powered by a battery which provides a direct current that flows in one direction at a constant rate

Question 21

Rules of a series circuit

Answer 21

Current is equal throughout
Current depends on the applied voltage
Voltage throughout the components add up to the voltage supplied
If one appliance fails, the whole circuit fails

Question 22

Rules of a parallel circuit

Answer 22

Voltage is equal throughout each loop
Current splits and the junctions. Total current at the junction equals the total current supplied
If one appliance fails, only that loop fails

Question 23

What is current

Answer 23

The rate of the flow of electrons

Question 24

What is voltage

Answer 24

The energy transferred per unit charge passed
ie.
1 volt = 1 joule per coulomb
20 V = 20 J per C

Question 25

What is Ohms law

Answer 25

(Only works for ohmic conductors) For conductor at a a constant temperature, the current is proportional to the voltage across it. Straight line in a I/V graph

Question 26

Give some examples of ohmic conductors

Answer 26

Wires | Resistors

Question 27

What is a non-ohmic conductor

Answer 27

Does not obey ohms law. Curved I/V graph

Question 28

Give some examples of non-ohmic conductors

Answer 28

``` Filament bulbs (because they heat up to much) Any type of diode Non-ohmic resistors (eg thermosister) ```

Question 29

Effect of resistance on current

Answer 29

More resistance = less current can flow

Question 30

Unit for current (I)

Answer 30

Amps - A

Question 31

How to LDRs work

Answer 31

Light dependant resistors | More light = less resistance

Question 32

How to thermistors work

Answer 32

More temperature = less resistance

Question 33

What are lamps and LED used to show

Answer 33

Lamps and LEDs are used to indicate the presence of currant in a circuit. More currant = brighter light

Question 34

Charge =

Answer 34

Q = I X t | Charge (C) = current (A) X time (s)

Question 35

What is an electric current

Answer 35

The flow of negatively charged electrons or of ions

Question 36

Common electrical conductors

Answer 36

Metals | Water

Question 37

Common electrical insulators

Answer 37

Plastic | Air

Question 38

What types of charges attract/repulse

Answer 38

Opposite charges attract (+/-) Similar charges repulse (+/+ or -/-) They do this because together they become neutral

Question 39

How are electrostatic charges produced

Answer 39

By the loss or gain of electrons Loss = positive charge Gain = negative charge

Question 40

Describe experiments to show how insulators can become charged by friction

Answer 40

Cloth on balloon, balloon becomes charged, balloon sticks to wall

Question 41

Explain the electrostatic phenomena in terms of the movement of electrons

Answer 41

Friction pulls electrons out of one object and into another

Question 42

Potential dangers of electrostatic charges

Answer 42

When refuelling. When a tanker moves through the air, the friction between the air and tanker causes the tanker to become charged. When you attach the metal nozzle to refuel, there could be a spark. This would ignite any fuel vapours causing a fire. To avoid this, and earthing wire is used

Question 43

Uses of electrostatic charges

Answer 43

Photocopiers Inkjet painting - all the pain droplets are given a similar charge (repeal each other forming a fine mist) and the car body is given an opposite charge (attracting the paint). This gives an even coating