CBSE Class 7 Science Heat Assignment

Question. A wet cloth was placed on a balance and left for several days. The change in its mass is shown in the graph below: What was the mass of WATER in the cloth at the start of the experiment?

(a) 60g
(b) 36g
(c) 24g
(d) 10g

Answer : B

Question. Identify this instrument.

(a) Compass
(b) Thermometer
(c) Car tyre pressure indicator
(d) Speedometer

Answer : B

Question. On a warm day, Suraj put a glass of cold water on the table and measured its temperature after every 2 minutes using an accurate thermometer. He made the table given below but forgot to record one reading. The temperature at 10:24 is most likely to be

(a) 14.5 (^oC)
(b) 15.5 (^oC)
(c) 16 (^oC)
(d) 17 (^oC)

Answer : C

Question. When a substance boils, it absorbs energy from the burning fuel. Which of these happens when a moth ball sublimes?
(a) Energy is neither absorbed nor released in the process.
(b) The moth ball absorbs energy from its surroundings
(c) The moth ball releases energy to its surroundings.
(d) The moth ball releases energy specifically to the air around it.

Answer : B

Question. An inventor claims that he has developed a fuel that is non-polluting and can be used as a petrol alternative. Which of these factors is NOT likely to influence its acceptance?
(a) Its performance in independent verification tests.
(b) The extent of change needed in existing car engines.
(c) The cost of the new fuel in comparison to the cost of petrol.
(d) Knowledge of the actual constituents of the new fuel.

Answer : D

Question. In the experiment shown a steel wire is tied to two chairs and kept taut. Two students sit, one on each chair. A weight is attached to the long wire with the help of a string and a pointer is attached to the weight to show the reading. What will happen to the arrow when the candles are lit?

(a) It will move up
(b) It will move down
(c) It will remain at the same position
(d) It will move up, then down" "

Answer : B

Question. Most substances expand when heated. See the picture of a thermometer before and after being heated slightly. What happens to the mercury and the glass when heated?

(a) The mercury expands and the glass contracts.
(b) The mercury expands; the glass neither expands nor contracts.
(c) The mercury neither expands nor contracts; the glass contracts.
(d) Both the mercury and the glass expand.

Answer : B

Question. Karuna takes some ice cubes from a freezer and places it in a bowl on a weighing scale. Which of these would show the position after 30 minutes?

Answer : B

Question. Students in a laboratory are told not to taste any chemicals (even common salt) in the laboratory. What is the MAIN reason?
(a) The chemicals used in the laboratory are not pure.
(b) Chemicals may have got mixed or wrongly labelled.
(c) The chemicals may get spoilt if they are touched.
(d) The chemical may get spoilt if they are touched.

Answer : B

Question. Which of these acids contains nitrogen?
(a) Sulphuric  acid (H₂SO₄)
(b) Acetic acid (CH₃COOH)
(c) Hydrochloric acid (HCl) 
(d) Nitric acid (HNO₃)

Answer : D

Question. The  three circles represent three types of substance as indicated. In which region of this figure should common salt be placed?

(a) P
(b) Q
(c) R
(d) S

Answer : B

Question. The hardness of a mineral represented by letter 'Q' is between
The Mohs Hardness scale represents the hardness of materials. Harder materials correspond to higher numbers in the scale. Harder materials can scratch softer materials. See the table below showing the hardness values of certain materials. Study the flow chart and answer the question.

(a) 7 and 8
(b) 6.5 and 7
(c) 5.5 and 6.5
(d) 3 and 5.5

Answer : C

Question. Which letter represents the softest mineral?
The Mohs Hardness scale represents the hardness of materials. Harder materials correspond to higher numbers in the scale. Harder materials can scratch softer materials. See the table below showing the hardness values of certain materials. Study the flow chart and answer the question.

(a) T
(b) S
(c) R
(d) Q

Answer : A

Question. Which of the following will result in a chemical change?
(a) Adding curd to milk
(b) Heating candle wax
(c) Mixing salt and water
(d) Adding water to milk

Answer : A

Question. Brass, an alloy of copper and zinc, is said to be a mixture, not a compound. Why is that?
(a) No new molecule is formed or exists in brass as compared to copper and zinc.
(b) No new molecule is formed or exists in brass as compared to copper and zinc.
(c) It is easy to perfectly separate brass into its constituents - copper and zinc.
(d) A metal cannot react chemically to form a compound with any other element.

Answer : B

I. Give one word for the following.

1) The degree of hotness or coldness of a body.

2) Metal used in thermometers.

3) Instrument used to measure temperature of a body.

4) Materials that allow heat to pass through them easily.

5) Materials that do not allow heat to pass through them.

I. Fill in the blanks.

1) Air is a ________ conductor of heat.

2) Solids ________ on cooling.

3) Heat is a form of energy that travels from a _______ object to a _______ object.

4) A spoon kept in a cup of hot tea gets heated by _________

5) The normal body temperature is _______ ^oC or _____^oF.

6) ________ is the best conductor of heat.

7) Ice melts at ______ ^oC or ______ ^oF.

8) Water boils at _______^oC or ______^oF.

9) Black bodies ________ and emit ________ heat the best.

10) The another name of clinical thermometer is __________ thermometer.

II. State true or false.

1) Heat cannot travel in vacuum.

2) Gases expand the most while solids expand the least on heating.

3) Room heaters warm the rooms by conduction.

4) Blankets keep us warm at night in winters.

5) The wooden handle of a pressure cooker prevents conduction of heat to the hand.

III. Match the following.

           A                   B

1) Conduction     a) day

2) Radiation        b) solids

3) Heat                c) night

4) Sea Breeze    d) energy

5) Land Breeze   e) vacuum

IV. Define.

i) Energy

ii) Temperature

iii) Conduction

iv) Convection

v) Radiation

V. Give reasons

i) Evaporation of sweat causes cooling.

ii) Ventilators are provided near the ceiling of a room.

iii) Clinical thermometers have a kink in the capillary tube

VI. Draw the diagram of the following:

i) Sea Breeze

ii) Land Breeze

HEAT

Question 1. Using the symbol segregate hot and cold objects :
 

Answer: Ice cream (Cold), Tea (Hot), Ice (Cold), Burning Candle (Hot).
In simple words: Objects with high temperature are hot, and objects with very low temperature are cold.

Exam Tip: Always categorize items based on their relative temperature compared to normal room temperature.

Question 2. State whether true of false :
1. The range of laboratory thermometer is from -10°C to 110°C.
Answer: True
In simple words: A standard laboratory thermometer typically measures temperatures from -10°C to 110°C.

Exam Tip: Remember that a clinical thermometer has a shorter range (35°C to 42°C) compared to a laboratory thermometer.

Question 2 (2). Temperature of our body can be measured by the help of clinical thermometer.
Answer: True
In simple words: Clinical thermometers are specifically designed to measure human body temperature.

Exam Tip: Clinical thermometers have a kink to prevent mercury level from falling on its own.

Question 2 (3). The materials which allow heat to pass through them easily are known as conductors.
Answer: True
In simple words: Conductors let heat move through them quickly, while insulators do not.

Exam Tip: Metals like copper, iron, and aluminium are good examples of conductors.

Question 2 (4). We use iron utensils to cook food, because iron is a good conductor of heat.
Answer: True
In simple words: Cooking utensils are made of metals like iron so they can efficiently transfer heat from the fire to the food.

Exam Tip: Good conductors are essential wherever quick heat transfer is needed.

Question 2 (5). We use woolen and dark coloured clothes during winter.
Answer: True
In simple words: Wool traps air and keeps us warm, while dark colors absorb heat from the sun.

Exam Tip: Wool is a poor conductor of heat (insulator), which prevents body heat from escaping.

Question 3. Fill in the blanks :
1. The normal temperature of human body is _____________.
Answer: \(37^{\circ}\text{C}\) (or \(98.6^{\circ}\text{F}\))
In simple words: A healthy human body maintains a standard average temperature of \(37^{\circ}\text{C}\).

Exam Tip: Always include the unit symbol (\(^{\circ}\text{C}\) or \(^{\circ}\text{F}\)) when writing temperature values.

Question 3 (2). Two insulators of heat are _______________, ______________.
Answer: Wood, Plastic (or Paper, Air, Rubber)
In simple words: Insulators are materials that do not allow heat to flow through them easily.

Question 3 (3). Two conductors of heat are ____________, _______________.
Answer: Iron, Copper (or Aluminium, Steel)
In simple words: Metals are generally good conductors of heat.

Exam Tip: Keep examples of common metals ready for conductor-based questions.

Question 3 (4). We use ________________ coloured clothes during summers.
Answer: Light
In simple words: Light-colored clothes reflect most of the heat radiation falling on them, keeping us cool.

Exam Tip: Contrast this with winter clothing, which relies on dark colors to absorb maximum heat.

Question 3 (5). We use woolen and ________________ coloured clothes during winter.
Answer: Dark
In simple words: Dark colors absorb heat and woolen fabric traps air to keep the body warm.

Exam Tip: Air trapped between wool fibers acts as an insulator.

Question 4. Match the following :
 

Answer:
1. - (d)
2. - (c)
3. - (b)
4. - (a)
In simple words: Land breeze occurs at night when land cools faster than sea, and sea breeze occurs during the day when land heats up faster.

Exam Tip: Remember that sea breeze blows from sea to land during the day, and land breeze blows from land to sea at night.

Question 5. Mark whether heat is transferred by conduction, convection or radiation :
Answer:
A. Radiation
B. Conduction
C. Convection
In simple words: Heat travels through space/air as radiation, through solid contact as conduction, and through fluid/liquid movement as convection.

Exam Tip: Identify the medium and state of matter: solids use conduction, fluids use convection, and open space/waves use radiation.