Topic 5 - Electricity and Circuits

Question 1

What is current?

Answer 1

The flow of electrical charge

Question 2

What is potential difference?

Answer 2

Energy transferred per unit charge

Question 3

What is resistance?

Answer 3

Anything that slows the flow of electrical charge down

Question 4

Finish the sentence: As temperature increases, resistance _________

Answer 4

Increases

Question 5

Why does resistance increase with temperature?

Answer 5

• Electrons collide with ions
• Ions are given some energy
• This means that the ions can vibrate
• Ions vibrating makes it hard for the electrons to flow through
• Thus, the resistance is higher at warmer temperatures

Question 6

What is the one exception to the resistance and temperature rule?

Answer 6

A thermistor, as its resistance decreases with an increase in temperature

Question 7

Describe the layout of a ‘standard test circuit’:

Answer 7

• d.c. power source with wires in both directions
• Ammeter connected to one end of power source
• Investigation component connected to the other end of the power source
• Voltmeter connected in parallel to the investigation component
• Investigation component and ammeter connected together

Question 8

How can you plot an I-V graph by using a ‘standard test circuit’?

Answer 8

• Connect the circuit
• Take one set of readings
• Change potential difference and record again
• Repeat 3-5 times
• Plot a graph of current against potential difference

Question 9

Describe the shape of an I-V graph for a fixed resistor:

Answer 9

Linear line through the origin

Question 10

Describe the shape of an I-V graph for a filament lamp:

Answer 10

• Shallow at bottom left
• Stepp through the middle
• Shallow at top right

Question 11

Describe the shape of an I-V graph for a diode:

Answer 11

Exponential graph shape

Question 12

What is an LDR?

Answer 12

Light-Dependant Resistor

Question 13

How does resistance change with an LDR?

Answer 13

• Low in bright light

- High in darkness

Question 14

How does resistance change with a thermistor?

Answer 14

• Low at high temperatures

- High at low temperatures

Question 15

Describe the layout of a series circuit:

Answer 15

All components connected together in a ring

Question 16

What is the main disadvantage of using a series circuit?

Answer 16

If one component is faulty, the whole circuit will fail

Question 17

Describe the layout of a parallel circuit:

Answer 17

Components connected to the power source separately - they appear to be in parallel lines, hence the name

Question 18

In a series circuit, how are current and potential difference shared?

Answer 18

• Current is equal everywhere

- Potential difference is split between components

Question 19

In a parallel circuit, how are current and potential difference shared?

Answer 19

• Current is split between components

- Potential difference is equal everywhere

Question 20

How does adding resistors have different effects in series and parallel circuits?

Answer 20

• In series, it increases total resistance

- In parallel, it decreases total resistance

Question 21

How is energy transferred when there is a change in potential difference?

Answer 21

Work is done against resistance

Question 22

Finish the sentence: Increasing the temperature of a circuit generally _______ its efficiency

Answer 22

Reduces

Question 23

In what situation is heating a circuit not too bad?

Answer 23

In appliances such as toasters which need to cook food, as the coils of wire have very high resistances

Question 24

What does energy transferred depend on?

Answer 24

Power

Question 25

Why would a microwave with a power rating of 500W cook slower than a microwave with a power rating of 750W?

Answer 25

Because less energy is transferred to the thermal energy store of the food per second, so it takes longer to increase and thus longer to cook

Question 26

What are the two types of electrical supply?

Answer 26

- Alternating current (a.c.) | - Direct current (d.c.)

Question 27

What type of electricity supply is mains supply?

Answer 27

a.c.

Question 28

What type of electricity supply is battery supply?

Answer 28

d.c.

Question 29

What are the three wires in a plug?

Answer 29

- Live wire - Neutral wire - Earth wire

Question 30

What are the potential differences of the three wires in a plug?

Answer 30

- Live wire: 230V - Neutral wire: 0V - Earth wire: 0V

Question 31

What does earthing prevent?

Answer 31

Electrical overloads

Question 32

What is the purpose of a fuse?

Answer 32

To protect the circuit in the plug

Question 33

How does a fuse work?

Answer 33

If the current is higher than the fuse rating, the fuse will melt. This breaks the circuit, so it can't work at an unsafe current. It will only work again if a new fuse is put into the plug