Heat CBSE Class 7

During a science experiment, Olivia noticed that when she placed a metal spoon in a hot cup of coffee, the spoon became warm. What is conduction of heat?

• Conduction of heat is the transfer of heat through direct contact between materials.

• Conduction of heat occurs only in gases.

• Conduction of heat is the movement of heat through fluids.

• Conduction of heat is the transfer of heat through radiation.

How does heat transfer through conduction occur?

• Heat transfer through conduction occurs via molecular collisions and energy transfer between adjacent molecules.

• Heat transfer through conduction is caused by the movement of fluids.

• Heat transfer through conduction occurs through radiation.

• Heat transfer through conduction happens via convection currents.

Which of the following is an example of conduction in a household setting?

• A metal frying pan heating on a stove.

• A wooden table in a sunny room.

• A plastic container left in the sun.

• A ceramic mug warming up with hot coffee.

What is convection in fluids?

• Convection is the process of heat transfer through solid materials.

• Convection is the transfer of heat through radiation without any fluid movement.

• Convection occurs only in gases and not in liquids.

• Convection is the transfer of heat in fluids through the movement of the fluid itself.

In a science class, Noah and Maya are discussing how heat is transferred in different materials. How does convection differ from conduction?

• Convection requires a solid medium; conduction does not need any medium.

• Convection is faster than conduction in all cases; conduction is slower.

• Convection occurs only in solids; conduction occurs in liquids and gases.

• Convection transfers heat through fluid movement; conduction transfers heat through direct contact.

Describe a real-life example of convection.

• Boiling water in a pot.

• Heating a room with a radiator.

• Ice melting in a glass of water.

• A fan blowing air in a room.

What is radiation of heat?

• Radiation of heat is the movement of air molecules carrying heat.

• Radiation of heat is the cooling of objects in a vacuum.

• Radiation of heat is the transfer of thermal energy through electromagnetic waves.

• Radiation of heat is the transfer of thermal energy through conduction.

What is the primary mechanism by which heat is transferred in a vacuum?

• Heat is transferred in a vacuum primarily through radiation, as there are no particles to conduct or convect heat.

• Conduction is the main method of heat transfer in a vacuum.

• Convection plays a significant role in heat transfer in a vacuum.

• Heat cannot be transferred in a vacuum at all.

Can you name a source of radiant heat?

• A microwave

• A refrigerator

• The sun

• A candle

During a hot summer day, Benjamin noticed that the metal slide in the playground became very warm. He wondered, what is thermal expansion?

• Thermal expansion is the decrease in size of a material due to an increase in temperature.

• Thermal expansion is the increase in size of a material due to an increase in temperature.

• Thermal expansion refers to the change in color of a material when heated.

• Thermal expansion is the process of cooling a material to reduce its size.