Electricity Y10

Question 1

What is voltage?

Answer 1

Energy transferred per unit charge passed

Volts = energy transferred ÷ charge

Question 2

What is current?

Answer 2

Rate of flow of charge

Amps = charge ÷ time

Question 3

What is resistance?

Answer 3

Ohms = voltage ÷ current

More resistance = less current.

Question 4

What is power?

Answer 4

Watts = energy ÷ time
Watts = voltage x current

Question 5

What does the current voltage graph of a resistor look like?

Answer 5

• straight line through origin ∴ V directly proportional to I
• constant gradient ∴ constant resistance
• constant resistance because constant temperature

Question 6

What does the current voltage graph of a bulb look like?

Answer 6

• s shape, with rotational symmetry
• at bottom gradient steep ∴ low resistance. This is due to low temperature, so the bulb will also be dimmer
• at top gradient shallow ∴ high resistance. This is due to high temperature, so bulb will be bright

Question 7

What does the current voltage graph of a diode look like?

Answer 7

• high resistance in one direction so current can only go in other direction
• only turns on at 0.6V

Question 8

What is a thermistor?

Answer 8

A resistors which varies with temperature. Cold = high res. Warm = low res.

Question 9

What is an LDR?

Answer 9

A resistor whose value depends on light intensity. Dark = high res. Light = low res.

Question 10

What order should you do circuit calculations in?

Answer 10

Resistance
Current
Voltage
Power

Question 11

What is the electron flow?

Answer 11

Negative to positive

Question 12

What is the current direction?

Answer 12

Positive to negative

Question 13

What is the difference between dc and ac?

Answer 13

Dc, e.g. Cell, only goes one way can’t change direction

Ac, e.g. Mains, goes both ways ∴ can change direction, above and below axis

Question 14

How can resistors be used in daily life?

Answer 14

• they slow down current ∴ the KE of the electrons turned into thermal energy
• can be used in appliance, e.g. Hair dryers

Question 15

How can you investigate how current varies w voltage in wires, resistors, lamps and diodes?

Answer 15

• use an ammeter and measure current w and wo these elements.
• measure different voltage levels using a voltmeter w these elements

Question 16

What is current like in series and parallel circuits?

Answer 16

Series: current is the same
Parallel: current divided by num of components

Question 17

How do you read an oscilloscope?

Answer 17

• x axis is time base- time per cm. Can find freq of wave: 1/time
• y axis is y-gain. This is volts per cm. We can work out the amplitude of the wave, e.g. If y-gain is 2 V/cm, and it is 3 cm high, then V = 6

Question 18

What does the earth wire do?

Answer 18

Longest pin ∴ goes in first and open other holes
If live wire becomes loose and touches the case, case becomes live. If you touch case, instead of current going through you, it takes path of least resistance through case, earth wire and to the ground ∴ creates a large current, which blows the fuse

Question 19

What is double insulation?

Answer 19

No external bits of metal in appliance ∴ case can’t become live ∴ don’t need earth wire

Question 20

What do the flex and cable grip do?

Answer 20

Flex is plastic coating on wire going in, as its an insulator
Cable grip: holds in flex and keeps it down

Question 21

What does the fuse do?

Answer 21

• if current going through it is too large it melts causing gap in circuit, thus preventing fire
Comes in 3A, 5A, and 13A. Use smallest possible, but only acc to 10%

Question 22

What does a circuit breaker do? What are its advantages over fuses?

Answer 22

• spring loaded switch held closed by soft iron bolt. An electromagnet is turned on if I too large and pulls bolt away ∴ switch opens and circuit breaks.
• more reliable (fuse only acc to 20%)
• more sensitive
• switch can be reset unlike fuse which breaks and so must be replaced
• respond mor rapidly to current surges than fuses

Question 23

What are the pros and cons of parallel circuits?

Answer 23

Pros: • can disconnect or connect new elements without disrupting other elements, e.g. Can turn off a light without all the lights in your house going off
• if one part breaks, it wont all. Current can flow through other parts
Cons: • can’t increase or decrease the voltage
• requires lots of wires

Question 24

What are the pros and cons of series circuits?

Answer 24

Pros: • more devices, the higher the voltage
• don’t overheat easily ∴ better around flammable things like clothes
Cons: • if one part breaks, it all breaks
• greater the num components, higher the resistance