IGCSE Electricity

Question 1

Describe the structure of an atom

Answer 1

Nucleus contains positively charged protons and neutral neutrons.
Negative electrons orbit the nucleus.

Question 2

How do objects become Negatively Charged?

Answer 2

• Electrons are transferred to the rod by friction.
• As the rod gains electrons it becomes negatively charged.
(NB The cloth loses electrons and becomes positively charged)

Question 3

How do objects become Positively charged?

Answer 3

• Friction removes electrons from the rod.
• As the rod looses electrons it becomes positively charged.
(NB The cloth gains electrons and becomes negatively charged.)

Question 4

How do Opposite Charges Behave?

Answer 4

Opposite charges ATTRACT.

Question 5

How do Like Charges Behave?

Answer 5

Like charges REPEL

Question 6

What happens to the resistance of a bulb as current increases.

Answer 6

The resistance of a lamp increases as the temperature increases.

Question 7

How does the resistance of a Thermistor change?

Answer 7

Low resistance when hot

High resistance when cold

Question 8

How does the resistance of a Light Dependant Resistor (LDR) change?

Answer 8

Low resistance when light

High resistance when dark

Question 9

What does an Ammeter measure and where should it be placed in a circuit?

Answer 9

An ammeter must be connected in series as it measures the current flowing through it.
Current is measured in Amps

Question 10

What does a Voltmeter measure and where should it be placed in a circuit?

Answer 10

A voltmeter must be connected in parallel as it measures the potential difference across the component.

Question 11

What is Ohm’s law?

Answer 11

The current is directly proportional to the voltage.

Fixed resistors and wires at constant temperature obey Ohm’s law.

Question 12

What is the function of a diode?

Answer 12

A diode allows current to flow in one direction only.

It has very high resistance to current in the reverse direction.

Question 13

What is the rule for currents in a parallel circuit?

Answer 13

The total current through the circuit is the sum of the current through the separate branches.

Question 14

What is the rule for currents in a series circuit?

Answer 14

The current is the same all the way around a series circuit.

Question 15

What is the rule for potential difference in a parallel circuit?

Answer 15

The potential difference across each branch is the same in a parallel circuit.

Question 16

What is the rule for potential difference in a series circuit?

Answer 16

In a parallel circuit the potential difference across each component adds up to the battery potential difference.

Question 17

What are some advantages of a parallel circuit?

Answer 17

In a parallel circuit:
• Switches can be used to control individual bulbs
• If one bulb breaks only the bulbs in the same branch will be affected
• Each bulb receives the same voltage so they if more are added they all stay bright.

Question 18

What are some disadvantages of a series circuit?

Answer 18

In a series circuit:
• If one bulb breaks they all go out (Christmas tree lights)
• One switch can be used to control all bulbs
• Voltage is shared so the more bulbs there are the dimmer they become.

Question 19

What is the definition of current?

Answer 19

Current is the rate of flow of charge.

Question 20

What is the definition of potential difference?

Answer 20

The potential difference across an electrical component is the electrical energy supplied to it per coulomb of charge flowing through it.

Question 21

What is the definition of emf?

Answer 21

The emf of a batter is the electrical energy it produces per coulomb of charge.

Question 22

What happens to the resistance of a wire if its cross sectional area is increased?

Answer 22

The larger the cross sectional area, the lower the resistance.

Question 23

What happens to the resistance of a wire if the length is increased?

Answer 23

The longer the wire the higher the resistance.