Electricity Updated

Question 1

What is current

Answer 1

• flow of electric charge
• carried by free electrons in a conductor
• measured in amperes using an ammeter
• can only flow through a closed circuit and when there is a potential difference

Question 2

What is potential difference

Answer 2

• tells us how much energy is transferred per coulomb of charge
• voltage

Question 3

What is resistance

Answer 3

• resistance slows the current down by collisions of electrons with atoms in the material
• higher resistance=lower current (for the same voltage)

Question 4

Ohms law

Answer 4

• v = ir
• only applies to ohmic conductors
• potential difference is directionally proportional to current

Question 5

Ohmic resistor graph

Answer 5

• straight line graph through origin
• obeys ohms law

Question 6

Filament lamp

Answer 6

• curves - resistance increases with temp
• gets hotter - atoms vibrate more - more collisions - resistance rises
• graph shaped like an f

Question 7

Diode

Answer 7

• only allows current in one direction
• in reverse direction: resistance is very high

Question 8

Series circuit

Answer 8

• current = same everywhere
• voltage = shared between components
• resistance = adds up (R1 + R2 + R3…)

Question 9

Disadvantage of series circuit

Answer 9

• if one component fails the whole circuit stops working

Question 10

Parallel circuit

Answer 10

• voltage = same across each branch
• current = splits between branches
• resistance = decreases as you add more branches: 1/R1 + 1/R2…

Question 11

Advantage of parallel circuit

Answer 11

Appliances can work independently

Question 12

Resistance required practical

Answer 12

• connect wire to circuit with voltmeter and ammeter
• use a thin wire on a ruler
• measure current + voltage at different lengths
• use r = v/i
• plot resistance vs length

Question 13

Conclusion of required practical

Answer 13

• resistance is directionally proportional to length
• ensure wire doesn’t heat up to much as it could affect accuracy

Question 14

DC

Answer 14

• direct current
• flows in one direction only
• supplied by cells or batteries
• graph: flat line at constant voltage

Question 15

AC

Answer 15

• alternating current
• current changes direction regularly
• supplied by UK main electricity
• graph: wave that oscillates above and below 0V

Question 16

Mains voltage and frequency

Answer 16

• voltage: 230V
• frequency: 50Hz

Question 17

Live wire

Answer 17

• brown
• carries current to appliance
• 230V

Question 18

Why is live wire dangerous

Answer 18

• even if a circuit is off, the live wire still carries 230V relative back to earth
• touching it = electric shock, as current flows through you to the ground

Question 19

Neutral wire

Answer 19

• blue
• completes circuit
• 0V

Question 20

Earth wire

Answer 20

• green/yellow stripes
• safety: prevents electric shock
• 0V (only carries current during fault)
• only needed for appliances with metal cases (double insulated appliances don’t need it)

Question 21

Fuses and circuit breakers

Answer 21

• fuses melt when current exceeds rating - break circuit
• circuit breakers detect surges and trip faster and can be reset
• prevent overheating and electric shocks

Question 22

What is the National grid

Answer 22

• transfers electricity from power stations to home and businesses efficiently

Question 23

Step-up transformer

Answer 23

• increases voltage and reduce current
• this means less energy is lost as heat in transmission cables

Question 24

Step-down transformers

Answer 24

• reduce voltage for safe use in homes

Question 25

Why is high voltage used in National grid

Answer 25

• because then theres a lower current so much less heat loss in wires

Question 26

Where do ammeter and voltmeter go in a parallel circuit

Answer 26

• ammeter goes in series
• voltmeter goes in parallel