Electricity and Magnetism Revision set 2

The ends of three metal rods are tested by holding end Q of rod 1 close to the others in turn. The results are as follows.

End Q attracts end R.

End Q attracts end S.

End Q attracts end T.

End Q repels end U.

Which of the metal rods is a magnet?

• rod 1 only

• rod 1 and rod 2

• rod 1 and rod 3

• rod 3 only

Answer explanation

Only the poles of a magnet can repel each other.

Which statement about a voltmeter is correct?

• A voltmeter measures the current in a component and is connected in series with the component.

• A voltmeter measures the current in a component and is connected in parallel with the component.

• A voltmeter measures the potential difference (p.d.) across a component and is connected in series with the component.

• A voltmeter measures the potential difference (p.d.) across a component and is connected in parallel with the component.

Answer explanation

A voltmeter measures the potential difference (p.d.) across a component and is connected in parallel with the component whereas an ammeter measures the current through a component and is connected in series.

A student sets up a circuit containing a battery of two cells and three lamps, as shown.

What is the circuit diagram for this arrangement?

• 
• 
• 
• 

The diagram shows a potential divider circuit.

The resistance of the variable resistor is increased.

What happens to the reading on voltmeter P and on voltmeter Q?

• reading on voltmeter P decreases

  reading on voltmeter Q decreases

• reading on voltmeter P decreases

  reading on voltmeter Q increases

• reading on voltmeter P increases

  reading on voltmeter Q decreases

• reading on voltmeter P increases

  reading on voltmeter Q increases

Answer explanation

If total resistance increases, current decreases so pd across fixed resistor decreases.

Total pd is the same so pd across variable resistor increases.

A current-carrying coil is placed in a magnetic field.

Which effect does the coil experience?

• a change in shape

• a change in weight

• a resultant force

• a turning effect

Answer explanation

The forces on each side of the coil are in opposite directions, so the coil turns.

In which circuit does the lamp light?

• 
• 
• 
• 

Answer explanation

A diode only allows current to flow if the "arrow" is pointing from positive terminal (longer line) to negative (shorter line).

Each potential divider is placed in a circuit with a power supply.

Which potential divider makes the potential difference across component Y increase when the light intensity increases?

• 
• 
• 
• 

Answer explanation

Component Y in this diagram is a thermistor - affected by temperature, not light intensity.

When light intensity increases the resistance of LDR decreases so current in circuit decreases. When LDR is X, pd across X decreases so pd across Y increases (as total pd does not change).

Which statement about the direction of a magnetic field at a point is correct?

• It is the direction of the force on a north pole placed at that point.

• It is the direction of the force on a south pole placed at that point.

• It is the direction of the force on a positive charge placed at that point.

• It is the direction of the force on a negative charge placed at that point.

Answer explanation

Key fact about magnetic field direction - goes from North to South Poles. (North pole would be repelled by another N & attracted to S)

The table shows the forces that exist between magnetic poles. Which row is correct?

• A

• B

• C

• D

Answer explanation

Like poles repel, unlike poles attract.

A polythene rod becomes negatively charged when it is rubbed with a cloth.

Which statement explains this?

• The rod gains electrons.

• The rod loses electrons.

• The rod gains protons.

• The rod loses protons.

Answer explanation

Only electrons (negative charge) move, NEVER protons.

An object becomes negatively charged when it gains electrons (like ions, in Chemistry)