10 Transfer of Heat and its Effects

What is the SI unit symbol for temperature?

• F

• R
• °C

• K

Answer explanation

The SI unit for temperature is Kelvin, represented by K.

Which of the following explains why a cup of bubble tea feel cold when we touch it?

• Our hands lose thermal (heat) energy as heat is transferred from our hands to the cup.

• Our hands lose thermal (heat) energy as heat is transferred from the cup to our hands.

• Our hands lose thermal (heat) energy as coldness is transferred from our hands to the cup.

• Our hands lose thermal (heat) energy as coldness is transferred from the cup to our hands.

Answer explanation

How we feel the temperature of an object is determined by the transfer of heat.

Recall that thermal energy is transferred from a region of higher temperature to a region of lower temperature.

We feel that something is hot when our hands gain heat. This happens when thermal energy is transferred from an object to our hand.

We feel that something is cold when our hands lose heat. This happens when thermal energy is transferred from our hand to an object.

What happens to a block of metal when it is heated and its temperature increases?

• Its density decreases as the block expands.

• Its density decreases as the block contracts.

• Its density increases as the block expands.

• Its density increases as the block contracts.

Train tracks often have gaps between them. This provide the necessary space for the (a)   of the tracks.

Which of the following are possible reasons for the increasing sea level?

• Global warming increases the temperature of oceans, causing the oceans to expand.

• Global warming results in the melting of glaciers, which increases the volume of water in the oceans.

• Global warming increases the temperature of oceans, causing the oceans to contract.

• Global warming results in the melting of glaciers, which decreases the volume of water in the oceans.

The image shows a bimetallic strip when it is heated.

Which of the following options explains why the bimetallic strip bends when there is a change in temperature?

• Brass has a higher mass compared to steel.

• Brass has a lower density compared to steel.

• Brass expands more compared to steel.

• Brass contracts more compared to steel.

Answer explanation

Brass and steel expand and contract at different rates.

When heated, brass expands more compared to steel. This expansion causes the strip to bend downwards to accommodate the additional length of the brass strip.

A hot air balloon is travelling with an altitude of 600m. What can be done to lower the altitude to 500m?

• Increase the intensity of the flame

• Decrease the intensity of the flame

Answer explanation

Substances of lower density float and substances of higher density sink.

To increase the density of the air in the hot air balloon, its temperature must be lowered. This causes the hot air to contract, decreasing its volume and thus, increasing its density.

Which of the following methods of heat transfer does not require a medium?

• Conduction

• Convection

• Radiation

Which of the following methods transfers thermal (heat) energy without physical movement of its medium?

• Conduction

• Convection

• Radiation

Answer explanation

Convection requires the physical movement of fluid (either liquid or gas).

Radiation does not involve a medium.

Which option explains why solids are better conductors of heat compared to fluids (liquids and gases)?

• The particles in a solid contain more energy compared to particles in a fluid.

• The particles in a solid are packed more closely to one another compared to particles in a fluid.

• The particles in a solid can move around the medium faster compared to particles in a fluid.

Answer explanation

Recall what you have learnt about the arrangement of particles in solids, liquids and gases.

In a solid, particles are packed very closely in an orderly manner. This allows the particles to transfer energy quickly from one particle to another.