Grade 9 Topics Part 2

How is latent heat defined?

• the thermal energy absorbed or emitted by unit mass during a change of state without a temperature change

• the thermal energy absorbed or emitted by unit mass during unit temperature change

• the thermal energy absorbed or emitted during a change of state without a temperature change

• the thermal energy absorbed or emitted during unit temperature change

In low-pressure hydrogen, there are no forces between the molecules except during collisions with each other.

Which statement describes the motion of a molecule between one collision and the next?

• It moves with changing speed and continuously changes direction.

• It moves with changing speed in a straight line.

• It moves with constant speed and continuously changes direction.

• It moves with constant speed in a straight line.

A gas is enclosed in a container of fixed volume.

The gas gains heat energy from an external source.

What happens to the molecules of the gas?

• They expand.

• They move faster inside the container.

• They move further apart.

• They vibrate with greater frequency.

A wave on water travels towards a stationary boat.

As the wave passes, the boat starts to move up and down and gains kinetic energy from the wave.

Which property of the wave changes as the wave passes the boat?

• amplitude

• frequency

• speed

• wavelength

Which waves are longitudinal?

• gamma rays

• light waves

• ultrasound waves

• X-rays

An object is placed at a distance from a converging lens that is equal to twice the focal length of the lens.

Which statement about the image is correct?

• It is enlarged.

• It is inverted.

• It is on the same side of the lens as the object.

• It is virtual.

The lens in the diagram produces an image I of the object O.

Why is this not the ray diagram for a photographic enlarger?

• The image is magnified.

• The image is virtual.

• The lens is converging lens.

• The lens is too thin.

The speed of sound in air is c_a, the speed of sound in water is c_w and the speed of sound in ice is c_i.

Which relationship is correct?

• c_a > c_i

• c_a > c_w

• c_i > c_w

• c_w = c_ia

The diagram shows a car ignition switch and starter motor.

The ignition switch is in a circuit with long, thin wires. The starter motor is in a circuit with short, thick wires.

What is the explanation for the choice of wires?

• Each circuit needs to contain the same total mass of wire.

• Thicker wires heat up more quickly when the relay is switched on.

• Thin wires have lower resistances.

• The ignition switch circuit carries a smaller current than the starter motor circuit.

The diagram shows a simple circuit.

What happens when the resistance of the variable resistor is increased?

• The lamps are dimmer and the motor rotates more quickly.

• The lamps are dimmer and the motor rotates more slowly.

• The lamps have the same brightness and the motor rotates more quickly.

• The lamps have the same brightness and the motor rotates more slowly.