Paper 1 - Electricity

Question 1

What is 1V?

Answer 1

1 joule per coulomb

Question 2

Why does a current in a resistor result in the electrical transfer of energy and an increase in temperature?

Answer 2

• Electrical energy is converted to thermal energy due to the resistance encountered by the moving electrons
• Increases temperature of the resistor
• Used in appliances where heat is the desired outcome

Question 3

How do circuit breakers protect the device or user in domestic appliances?

Answer 3

• Circuit breaker opens when too much current in being carried by the wire
• Causes an open circuit
• Current cannot flow through an open/broken circuit

Question 4

How does earthing protect the device or user in domestic appliances?

Answer 4

• Made of copper
• Low resistance path to the ground
• Connected to the casing of electrical devices

Question 5

Why is current conserved at a junction in a circuit?

Answer 5

• Principal of conservation of electric charge
• At any point in a circuit, the number of electrons entering the junction must be equal to the number of electrons leaving the junction

Question 6

How do fuses protect the device or user in domestic appliances?

Answer 6

• Made of a substance with a lower boiling point
• Will melt if a circuit is carrying too much charge
• Melted fuse will break the circuit so current cannot flow

Question 7

What is the relationship between power, current and voltage?

Answer 7

P = IV

Question 8

What is the relationship between energy transferred, current, voltage and time?

Answer 8

E = ItV

Question 9

What is the difference between a.c. and d.c.?

Answer 9

• a.c. is main electricity being alternating current
• d.c. is electricity from a cell or battery being direct current
• a.c. is @50Hz so changes direction 50 times per second, d.c. does not

Question 10

Why is a series circuit better for some appliances?

Answer 10

When it is ideal to have:

• Same current everywhere
• Shared voltage across components

Question 11

Why is a parallel circuit better for some appliances?

Answer 11

When it is ideal to have:

• Shared current across components
• Same voltage everywhere

Question 12

How does the current in a series circuit depend on the applied voltage and the number/nature of other components?

Answer 12

• Ohms law - I = V / Rtotal
• The current in a circuit is directly proportional to the voltage
• The current in a circuit is inversely proportional to the total resistance

Question 13

What is the effect of changing the resistance on the current in a circuit?

Answer 13

• Increase in resistance = decrease in current
• Decrease in resistance = increase in current
• Current and resistance are inversely proportional

Question 14

Describe the variation of resistance in LDR’s

Answer 14

• Increase in light = decrease in resistance
• Decrease in light = increase in resistance
• Current and light are inversely proportional

Question 15

Describe the variation of resistance in thermistors

Answer 15

• Increase in temperature = decrease in resistance
• Decrease in temperature = increase in resistance
• Current and temperature are inversely proportional

Question 16

What can lamps and LEDs be used for in a circuit?

Answer 16

Indicating the presence of current in a circuit

Question 17

What is the relationship between voltage, current and resistance?

Answer 17

V = IR

Question 18

What is the relationship between charge, current and time?

Answer 18

Q = It

Question 19

What is electrical current in solid metal conductors?

Answer 19

A flow of negatively charged electrons

Question 20

What is voltage?

Answer 20

The energy transferred per unit of charge passed

Question 21

How does double insulation protect the device or user in domestic appliances?

Answer 21

• Used in appliances with plastic exteriors that do not have earthing
• 2 layers of non-conductive materials
• Only used to cover live parts

Question 22

How does insulation protect the device or user in domestic appliances?

Answer 22

• Plastic or non-conductive material wrapped around all 3 wires
• Used to protect the appliance or user if a wire comes loose

Question 23

How is the voltage across 2 components in parallel distributed?

Answer 23

The voltage is equal

Question 24

How is the voltage across 2 components in series distributed?

Answer 24

It is shared between them

Question 25

What is current?

Answer 25

The rate of flow of charge

Question 26

What is the relationship between energy transferred, charge and voltage?

Answer 26

E = QV

Question 27

How does voltage vary in wires?

Answer 27

• Voltage increases with current
• They are directly proportional

Question 28

How does voltage vary in resistors?

Answer 28

• Voltage increases with current
• They are directly proportional

Question 29

How does voltage vary in metal filament lamps?

Answer 29

• As voltage increases, the current initially increases
• But current increases at a faster rate due to the heating of the filament

Question 30

How does voltage vary in diodes?

Answer 30

• When voltage exceeds Vf the voltage in a diode increases significantly
• The increases in not linear, it is exponential

Question 31

Why does a lamp receiving more current mean that it is brighter?

Answer 31

• because power = current × voltage
• voltage is the same for all lamps
• current is greatest