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CLASS VII SCIENCE
CLASS VII SCIENCE
CHAPTER VII: HEAT TRANSFER IN NATURE
CHAPTER VII: HEAT TRANSFER IN NATURE
Direct Questions Assertion / Reason Correct / Incorrect HOTS Challenging
DIRECT QUESTIONS
DIRECT QUESTIONS
Heat flows from an object at a ________ temperature to an object at a ________ temperature.
A. Lower, Higher
B. Higher, Lower
C. Same, Higher
D. Higher, Same
Answer: B. Higher, Lower
The process by which heat is transferred from the hotter end to the colder end of an object without the actual movement of its particles is:
A. Convection
B. Radiation
C. Conduction
D. Insulation
Answer: C. Conduction
Which of the following is a good conductor of heat?
A. Wood
B. Plastic
C. Iron
D. Wool
Answer: C. Iron
The transfer of heat in liquids and gases takes place primarily through:
A. Conduction
B. Convection
C. Radiation
D. Absorption
Answer: B. Convection
The transfer of heat that does not require any medium is called:
A. Conduction
/B. Convection
C. Radiation
D. Insulation
Answer: C. Radiation
In coastal areas, during the day, the air above the land gets hotter and rises up. The cooler air from the sea rushes in towards the land. This is called:
A. Land breeze
B. Sea breeze
C. Trade winds
D. Cyclone
Answer: B. Sea breeze
At night, the land cools down faster than the sea. The cool air from the land moves towards the sea. This is called:
A. Sea breeze
B. Land breeze
C. Monsoon
D. Tsunami
Answer: B. Land breeze
Dark-colored surfaces ________ more heat than light-colored surfaces.
A. Reflect
B. Absorb
C. Conduct
D. Radiate
Answer: B. Absorb
We prefer to wear ________ clothes in summer.
A. Dark-colored
B. Light-colored
C. Woolen
D. Silk
Answer: B. Light-colored
Woolen clothes keep us warm in winter because:
A. Wool is a good conductor of heat
B. Air trapped between wool fibers is a poor conductor of heat
C. Wool reflects body heat
D. Wool absorbs sunlight
Answer: B. Air trapped between wool fibers is a poor conductor of heat
A stainless steel pan is usually provided with a copper bottom because:
A. Copper makes the pan look more colorful
B. Copper is a better conductor of heat than stainless steel
C. Copper is easier to clean
D. Copper is cheaper
Answer: B. Copper is a better conductor of heat than stainless steel
The vacuum in a thermos flask prevents heat loss by:
A. Conduction only
B. Convection only
C. Both Conduction and Convection
D. Radiation only
Answer: C. Both Conduction and Convection
Ventilators in houses are provided near the ceiling because:
A. It looks good
B. Hot air, being lighter, rises up and goes out
C. To let in more sunlight
D. To prevent rain from entering
Answer: B. Hot air, being lighter, rises up and goes out
Which of the following is the best insulator of heat?
A. Copper
B. Aluminum
C. Air
D. Silver
Answer: C. Air
What happens to the level of mercury in a thermometer when it is placed in hot water?
A. It falls
B. It rises
C. It remains the same
D. It turns blue
Answer: B. It rises
One kilometer above the Earth's surface, the atmosphere is heated mainly by:
A. Conduction from the ground
B. Convection currents in the air
C. Direct radiation from the sun
D. Friction
Answer: B. Convection currents in the air
Why is the handle of a pressure cooker made of ebonite or plastic?
A. To make it heavy
B. Because they are poor conductors of heat (insulators)
C. To make it shine
D. Because they are metals
Answer: B. Because they are poor conductors of heat (insulators)
The boiling point of water at sea level is:
A. 0°C
B. 37°C
C. 100°C
D. 212°C
Answer: C. 100°C
Heat from the Sun reaches the Earth through:
A. Conduction
B. Convection
C. Radiation
D. The atmosphere only
Answer: C. Radiation
A marble tile feels colder than a wooden floor in winter because the marble tile:
A. Is a better conductor of heat than wood
B. Is a poorer conductor of heat than wood
C. Reflects more heat than wood
D. Is at a lower temperature than wood
Answer: A. Is a better conductor of heat than wood
When two objects are at the same temperature, the heat transfer between them:
A. Continues at a fast rate
B. Stops
C. Moves only from left to right
D. Becomes radiation only
Answer: B. Stops
Which mode of heat transfer involves the actual movement of molecules?
A. Conduction
B. Convection
C. Radiation
D. None of the above
Answer: B. Convection
Black umbrellas are often used in summer because:
A. They reflect heat
B. They are fashionable
C. They absorb heat on the outside and prevent it from reaching the person (if double-layered)
D. They are cheaper
Answer: C. They absorb heat on the outside and prevent it from reaching the person (if double-layered)
A clinical thermometer can measure temperatures from:
A. 0°C to 100°C
B. 35°C to 42°C
C. -10°C to 110°C
D. 32°F to 212°F
Answer: B. 35°C to 42°C
The normal temperature of a healthy human body is:
A. 35°C
B. 37°C
C. 40°C
D. 98.6°C
Answer: B. 37°C
Sea breeze blows during the:
A. Night
B. Day
C. Evening
D. All the time
Answer: B. Day
The range of a laboratory thermometer is usually:
A. 35°C to 42°C
B. 0°C to 100°C
C. -10°C to 110°C
D. 37°C to 38°C
Answer: C. -10°C to 110°C
Which of the following substances does not conduct heat through convection?
A. Water
B. Air
C. Iron rod
D. Molten wax
Answer: C. Iron rod
Why do birds puff up their feathers in winter?
A. To look bigger
B. To fly better
C. To trap more air, which acts as an insulator
D. To scare predators
Answer: C. To trap more air, which acts as an insulator
Heat is a form of:
A. Matter
B. Energy
C. Power
D. Force
Answer: B. Energy
Solids generally transfer heat by:
A. Conduction
B. Convection
C. Radiation
D. Evaporation
Answer: A. Conduction
A liquid used in thermometers should have:
A. High freezing point
B. Low boiling point
C. Uniform expansion
D. Dark color
Answer: C. Uniform expansion
Solar cookers are painted black from the inside to:
A. Prevent rusting
B. Absorb maximum heat
C. Reflect sunlight
D. Look clean
Answer: B. Absorb maximum heat
A bird sitting on a high-tension wire does not get a shock, but if it touches two wires, it does. This relates to:
A. Conduction
B. Radiation
C. Potential difference
D. Convection
Answer: C. Potential difference
The "kink" in a clinical thermometer:
A. Makes it look stylish
B. Prevents the mercury level from falling on its own
C. Helps the mercury to rise faster
D. Is used for cleaning
Answer: B. Prevents the mercury level from falling on its own
Which of the following is a poor conductor of heat?
A. Silver
B. Copper
C. Distilled water
D. Aluminum
Answer: C. Distilled water
Firefighters wear shiny suits to:
A. Be seen easily
B. Reflect the heat radiation from the fire
C. Keep themselves warm
D. Absorb smoke
Answer: B. Reflect the heat radiation from the fire
Ice is wrapped in gunny bags to:
A. Keep it clean
B. Prevent it from melting by insulating it from outside heat
C. Make it easy to carry
D. Make it freeze faster
Answer: B. Prevent it from melting by insulating it from outside heat
Cooking utensils are often made of metals because they:
A. Are very strong
B. Are good conductors of heat
C. Do not melt easily
D. All of the above
Answer: D. All of the above
Heat radiation travels at the speed of:
A. Sound
B. Light
C. Electricity
D. Wind
Answer: B. Light
ASSERTION AND REASON
ASSERTION AND REASON
A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true but R is not the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.
Assertion (A): We wear woolen clothes in winter.
Reason (R): Wool is a good conductor of heat.
Answer: C. A is true but R is false.
Assertion (A): Sea breeze blows during the day in coastal areas.
Reason (R): Land gets heated faster than the sea during the daytime.
Answer: A. Both A and R are true and R is the correct explanation of A.
Assertion (A): Clinical thermometers have a short range of temperature.
Reason (R): The temperature of the human body does not vary beyond 35°C to 42°C.
Answer: A. Both A and R are true and R is the correct explanation of A.
Assertion (A): Heat from the Sun cannot reach us by conduction or convection.
Reason (R): Most of the space between the Sun and the Earth is a vacuum.
Answer: A. Both A and R are true and R is the correct explanation of A.
Assertion (A): Dark-colored clothes are preferred in summer.
Reason (R): Dark colors reflect most of the heat that falls on them.
Answer: D. A is false but R is true (Note: R is technically false as stated, but A is definitely false).
Assertion (A): Air is a poor conductor of heat.
Reason (R): Two thin blankets are warmer than one thick blanket of the same total thickness.
Answer: A. Both A and R are true and R is the correct explanation of A.
Assertion (A): Land breeze blows from sea to land.
Reason (R): Land cools faster than sea at night.
Answer: D. A is false but R is true.
Assertion (A): A stainless steel pan with a copper bottom is more efficient.
Reason (R): Copper is a better conductor of heat than stainless steel.
Answer: A. Both A and R are true and R is the correct explanation of A.
Assertion (A): Convection occurs only in solids.
Reason (R): Particles in solids are tightly packed and cannot move.
Answer: D. A is false but R is true.
Assertion (A): The kink in a clinical thermometer is very important.
Reason (R): It allows the mercury level to be read at leisure after removing it from the mouth.
Answer: A. Both A and R are true and R is the correct explanation of A.
CORRECT / INCORRECT STATEMENTS
CORRECT / INCORRECT STATEMENTS
Which of the following statements is INCORRECT?
A. Conduction requires a medium.
B. Convection takes place in a vacuum.
C. Radiation does not require a medium.
D. Solids are generally heated by conduction.
Answer: B. Convection takes place in a vacuum.
Identify the CORRECT statement:
A. Silver is a poor conductor of heat.
B. Land breeze blows during the day.
C. A laboratory thermometer should be held tilted while reading.
D. Digital thermometers do not use mercury.
Answer: D. Digital thermometers do not use mercury.
Which of the following about heat transfer is CORRECT?
A. Heat flows from cold to hot bodies.
B. Conduction is the main mode of heat transfer in gases.
C. All hot bodies radiate heat.
D. Sea breeze is caused by conduction.
Answer: C. All hot bodies radiate heat.
Find the INCORRECT statement:
A. Woolen clothes keep us warm.
B. White clothes absorb more heat than black clothes.
C. Mercury is used in thermometers because it is a metal in liquid state.
D. Ventilators are provided at the top of rooms.
Answer: B. White clothes absorb more heat than black clothes.
Which statement about thermometers is CORRECT?
A. Clinical thermometer is used for boiling milk.
B. Laboratory thermometer can be used to measure body temperature if read quickly.
C. We should not wash a clinical thermometer in hot water.
D. Mercury is a non-toxic substance.
Answer: C. We should not wash a clinical thermometer in hot water.
HOTS (HIGHER ORDER THINKING SKILLS)
HOTS (HIGHER ORDER THINKING SKILLS)
Why does a desert cool down so quickly at night?
A. Sand is a good conductor.
B. Sand absorbs and radiates heat very quickly, and there is no moisture to trap the heat.
C. The wind is very strong.
D. Deserts are close to the poles.
Answer: B. Sand absorbs and radiates heat very quickly, and there is no moisture to trap the heat.
Why are double-walled glass windows used in cold countries?
A. To make them stronger.
B. To trap a layer of air, which acts as an insulator and keeps the room warm.
C. To prevent birds from hitting the glass.
D. To reflect sunlight.
Answer: B. To trap a layer of air, which acts as an insulator and keeps the room warm.
If you are given a choice in winter of using either one thick blanket or two thin blankets joined together, which one would you choose?
A. One thick blanket because it is heavier.
B. Two thin blankets because the layer of air trapped between them provides extra insulation.
C. Either one, it doesn't matter.
D. One thick blanket because air is a good conductor.
Answer: B. Two thin blankets because the layer of air trapped between them provides extra insulation.
Why is the heating element of an electric kettle placed at the bottom?
A. To save space.
B. To heat the water at the bottom, which then rises up due to convection, heating the entire volume.
C. To prevent the handle from getting hot.
D. Because the bottom is made of plastic.
Answer: B. To heat the water at the bottom, which then rises up due to convection, heating the entire volume.
Why do we feel warm when we sit near a fire?
A. Due to conduction of air.
B. Due to convection of air.
C. Due to radiation from the fire.
D. Due to direct contact.
Answer: C. Due to radiation from the fire.
CHALLENGING QUESTIONS
CHALLENGING QUESTIONS
In which of the following cases will the heat transfer be fastest?
A. Between 10°C and 20°C
B. Between 10°C and 40°C
C. Between 50°C and 60°C
D. Between 20°C and 30°C
Answer: B. Between 10°C and 40°C (Greater temperature difference).
If a person has a temperature of 104°F, what is their temperature in Celsius?
A. 37°C
B. 40°C
C. 42°C
D. 45°C
Answer: B. 40°C [Using $C = (F - 32) \times 5/9$]
What happens to the temperature of a mixture of 1 liter of water at 30°C and 1 liter of water at 50°C?
A. It becomes 80°C.
B. It becomes more than 50°C.
C. It will be between 30°C and 50°C.
D. It becomes 20°C.
Answer: C. It will be between 30°C and 50°C.
Which of the following is NOT a consequence of convection?
A. Sea breeze
B. Land breeze
C. Trade winds
D. Heating of a metal spoon in hot tea
Answer: D. Heating of a metal spoon in hot tea (This is conduction).
A black body and a white body are kept in the sun for the same amount of time. Then they are moved to a dark, cold room. Which one will cool down faster?
A. The white body.
B. The black body.
C. Both will cool at the same rate.
D. Neither will cool.
Answer: B. The black body (Good absorbers are also good radiators).
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