IMO Practice Test: Heat, Light and Sound | Class 7 Physics

Question 1 of 35

Which of the following scenarios violates the concept of heat flow?

Ice melts in a warm room

A hot pan cools on a metal counter

A cold spoon becomes colder when placed in hot soup

Warm air rises from a radiator

Explanation: A cold spoon must gain heat from hot soup and become warmer. Becoming colder would mean heat flows from cold to hot, which is impossible.

Question 2 of 35

Two beakers contain equal mass of water. Beaker A is at 40°C. Beaker B is at 20°C. You add the same amount of heat to both. Which will have a higher final temperature?

Beaker A

Beaker B

Both same

Depends on room temperature

Explanation: Equal mass and substance means each beaker rises by the same ΔT. A started higher (40 + ΔT) than B (20 + ΔT), so A stays higher.

Question 3 of 35

A scientist says: "Two objects in contact reached the same temperature, but heat continues to flow." Is this possible?

Yes, if one is larger

Yes, if one is metal

No, heat stops when temperatures equal

Yes, if they are in vacuum

Explanation: Thermal equilibrium means no net heat flow. When temperatures are equal, heat stops flowing on average.

Question 4 of 35

Which unit is used for both heat energy and other forms of energy like work?

Watt

Degree

Joule

Kelvin

Explanation: Joule (J) is the SI unit for all forms of energy, including heat, work, kinetic energy, etc.

Question 5 of 35

A 100 g iron nail at 200°C is dropped into 1 kg of water at 25°C. The final temperature is 26°C. What can you conclude?

Water gained more heat than iron lost

Iron lost more heat than water gained

Heat lost by iron = heat gained by water

Temperature of iron did not change

Explanation: Law of conservation of energy: heat lost by hot object = heat gained by cold object (assuming no heat loss to surroundings).

Question 6 of 35

A clinical thermometer reads 40°C. The patient's actual temperature is 39°C. What could have caused this?

The thermometer was not shaken before use

The kink is broken

Mercury expanded too much

Room temperature was high

Explanation: If the previous reading was 40°C and the thermometer was not shaken to reset it below 35°C, it will still show 40°C even if the patient is cooler.

Question 7 of 35

Two thermometers — one with mercury and one with alcohol — are placed in the same water. Mercury rises to 70°C. Alcohol rises to 70°C as well. What can you conclude?

Mercury thermometer is faulty

Alcohol thermometer is faulty

Both are accurate

Water temperature is 70°C

Explanation: Both thermometers are calibrated correctly. If both show the same reading, that is the actual temperature.

Question 8 of 35

At what temperature do Celsius and Fahrenheit scales show the same number?

0°

32°

−40°

100°

Explanation: Solve C = (C × 9/5) + 32 → C − (9C/5) = 32 → (5C−9C)/5 = 32 → (−4C)/5 = 32 → C = −40. At −40°, both scales read the same.

Question 9 of 35

A laboratory thermometer has 10 divisions between 30°C and 40°C. What is the least count?

0.5°C

1°C

0.1°C

2°C

Explanation: Range = 10°C. Number of divisions = 10. Least count = 10/10 = 1°C.

Question 10 of 35

Why is alcohol sometimes used instead of mercury in very cold regions?

Alcohol is cheaper

Alcohol freezes at −115°C, mercury freezes at −39°C

Alcohol expands more

Alcohol is safer to drink

Explanation: In extremely cold places like Siberia, temperatures can drop below −40°C. Mercury would freeze, but alcohol remains liquid.

Question 11 of 35

A metal rod is heated at one end. After some time, the other end becomes hot. Which statement correctly describes the process?

Heat travels as waves

Particles move from hot end to cold end

Particles vibrate and pass energy to neighbors

Hot air carries heat along the rod

Explanation: In conduction, particles do not move from place to place; they vibrate and transfer energy through collisions.

Question 12 of 35

A room has a radiator near the ceiling. The room does not warm up well. Why?

Radiators emit only radiation

Hot air stays at ceiling and does not reach floor

Conduction is poor in air

The radiator is too small

Explanation: Heaters should be placed near the floor because hot air rises. If placed near ceiling, hot air stays up and cold air stays down.

Question 13 of 35

Which surface is best for absorbing radiant heat?

Polished silver

White painted

Dull black

Transparent glass

Explanation: Dull black surfaces are the best absorbers of radiation. Shiny surfaces reflect radiation.

Question 14 of 35

On a cold night, a glass window feels colder than the wooden door frame even though both are at the same temperature. Why?

Glass has lower temperature

Wood is a better conductor

Glass conducts heat away from your hand faster

Wood radiates more heat

Explanation: Glass is a better conductor than wood. It pulls heat from your hand faster, making it feel colder.

Question 15 of 35

In which of these situations is heat transferred primarily by radiation?

Frying an egg on a pan

Warm air rising from a desert

Feeling heat from a campfire from 5 meters away

An iron rod in a furnace

Explanation: At a distance, conduction and convection are negligible. Radiation from the fire travels directly to you.

Question 16 of 35

A student touches a metal rod and a wooden rod that have been sitting in a freezer at −10°C. Which statement is correct?

Both feel equally cold

The metal rod feels colder because it conducts heat faster

The wooden rod feels colder because it stores more cold

Neither feels cold because the room is warm

Explanation: Metal conducts heat away from the hand faster than wood. "Cold" is the sensation of heat leaving your body.

Question 17 of 35

A house in a desert has thick mud walls. The mud walls keep the inside cool during the day and warm at night. Why?

Mud is a conductor

Mud is an insulator with high thermal mass

Mud reflects all radiation

Mud produces heat at night

Explanation: Mud is a poor conductor (insulator). It heats up slowly during the day and cools down slowly at night, reducing temperature swings. This is called "thermal mass" or "thermal inertia."

Question 18 of 35

Which combination of materials would make the BEST thermos flask to keep coffee hot for 12 hours?

Metal inner + metal outer + no vacuum

Glass inner + glass outer + vacuum + silver coating

Plastic inner + plastic outer + air layer

Copper inner + copper outer + black coating

Explanation: Vacuum stops conduction and convection; silver coating reflects radiation; glass is also a poor conductor. This is exactly how a real thermos works.

Question 19 of 35

Why are electrical wires that carry current covered with plastic or rubber?

To make them look neat

Plastic and rubber are conductors

Plastic and rubber are insulators that prevent electric shock and heat loss

To make them heavier

Explanation: Plastic and rubber are electrical and thermal insulators. They prevent electric shock and also prevent heat from escaping (or entering) the wire.

Question 20 of 35

In a traditional Japanese house, floors are covered with tatami mats (made of rice straw and rush grass). Why do these mats feel warm to bare feet in winter even though the room is cold?

The mats generate heat

The mats are good insulators and prevent heat loss from feet

The mats are good conductors and bring heat from the ground

The mats are at a higher temperature than the air

Explanation: The mats are insulators, so when you step on them, your body heat does not flow away quickly. They feel warm because heat is trapped near your skin.

Question 21 of 35

A coastal city has a temperature of 35°C at 2 PM. An inland city at the same latitude has 42°C. Which is the most likely reason?

Inland city has more pollution

Sea breeze cools the coastal city

Land breeze cools the coastal city

Coastal city has darker soil

Explanation: Sea breeze brings cool ocean air to coastal city during afternoon, reducing temperature compared to inland.

Question 22 of 35

Which statement about land breeze is TRUE?

It occurs when land is warmer than sea

It occurs only during full moon

It occurs when sea is warmer than land

It blows from sea to land

Explanation: Land breeze occurs at night when sea is warmer than land, so wind blows from land to sea.

Question 23 of 35

A student claims: "Sea breeze is stronger in summer than in winter." Is this correct?

Yes, because temperature difference is larger in summer

No, sea breeze is stronger in winter

Sea breeze does not occur in summer

Sea breeze strength is same all year

Explanation: In summer, land becomes much hotter than sea, creating a large temperature difference → stronger sea breeze.

Question 24 of 35

Why does land heat up faster than water? (Choose the BEST reason.)

Land is darker in color

Water has higher specific heat capacity and mixing currents

Land is closer to the Sun

Water reflects more sunlight

Explanation: Water has high specific heat (takes more energy to warm) and also mixing currents distribute heat downward.

Question 25 of 35

At 6 AM on a beach, the air temperature over land is 18°C and over sea is 22°C. Which direction will the wind blow?

Sea to land

Land to sea

Upward

No wind

Explanation: Land (18°C) is cooler than sea (22°C). Cooler air over land is denser and flows towards warmer sea → land breeze.

Question 26 of 35

Two rods — one made of steel and one made of brass — are exactly the same length at 20°C. They are heated to 100°C. Which rod will be longer? (Steel expands less than brass.)

Steel rod

Brass rod

Both remain equal

Depends on room temperature

Explanation: Brass has a higher coefficient of thermal expansion than steel, so it expands more for the same temperature increase.

Question 27 of 35

A concrete sidewalk has gaps every few meters. In summer, the gaps almost disappear. In winter, they become wider. Why?

Concrete expands in summer, contracts in winter

Concrete contracts in summer, expands in winter

Gaps fill with dirt in summer

The sidewalk moves due to earthquakes

Explanation: Concrete expands when hot (summer), closing the gaps; contracts when cold (winter), widening the gaps.

Question 28 of 35

A metal ball has a diameter of 5.00 cm at 20°C. Its coefficient of linear expansion is 0.000019 per °C. What is its approximate diameter at 120°C?

5.0095 cm

5.0000 cm

5.095 cm

4.995 cm

Explanation: Expansion = original length × coefficient × ΔT = 5 × 0.000019 × 100 = 0.0095 cm. New length = 5.0095 cm.

Question 29 of 35

Why does a tightly closed glass bottle filled completely with water sometimes crack when left in a freezer?

Water expands when freezing

Glass contracts more than water

Freezer is too cold

The bottle cap shrinks

Explanation: Water expands as it freezes (anomalous expansion). The expanding ice exerts pressure on the glass, causing it to crack.

Question 30 of 35

A thermostat uses a bimetallic strip to turn a heater on and off. As the room cools, the strip straightens and completes an electrical circuit. Which metal is on the outside when the strip is bent in a warm room?

Metal with lower expansion

Metal with higher expansion

Both metals expand equally

Cannot be determined

Explanation: In a warm room, the bimetallic strip is bent. The metal with higher expansion is on the outside of the bend (longer arc). As the room cools, the strip straightens.

Question 31 of 35

10 g of ice at 0°C is mixed with 100 g of water at 30°C. The final temperature is 20°C. What can you conclude?

Ice did not melt completely

Ice melted completely and then water warmed

No heat was exchanged

The experiment was done in a vacuum

Explanation: The final temperature is above 0°C, so all ice melted. The ice absorbed latent heat to melt and then sensible heat to warm to 20°C.

Question 32 of 35

Why does a pressure cooker cook food faster than an open pot?

Higher pressure increases latent heat of vaporization

Higher pressure raises boiling point, so food cooks at higher temperature

Pressure cooker has less water

Pressure cooker is made of metal

Explanation: Higher pressure means water boils at >100°C. Higher cooking temperature means faster cooking.

Question 33 of 35

Which statement about latent heat is TRUE?

Latent heat can be measured with a thermometer

Latent heat causes temperature to rise

Latent heat is absorbed or released during state changes without temperature change

Latent heat only applies to water

Explanation: This is the definition of latent heat. Temperature remains constant during the state change.

Question 34 of 35

A cold drink has ice cubes floating in it. After 10 minutes, the ice cubes have melted but the drink temperature is still 0°C. Where did the heat to melt the ice come from?

From the surrounding air only

From the drink itself

From the glass

From the ice cubes themselves

Explanation: The drink (liquid) was above 0°C initially. It gave up its heat to melt the ice, cooling itself down to 0°C in the process.

Question 35 of 35

You have two identical burners. You put 1 kg of ice at 0°C on one and 1 kg of water at 0°C on the other. Which will reach 100°C first? (Both receive same heat per second.)

The ice will reach first

The water will reach first

Both reach at same time

Cannot be determined

Explanation: Ice must first absorb latent heat (334,000 J) to melt into water at 0°C, then heat from 0°C to 100°C. Water at 0°C only needs to heat from 0°C to 100°C. The water wins by 334,000 J worth of time.

IMO Practice Test — Heat, Light and Sound