Gujarat Board GSEB Textbook Solutions Class 7 Science Chapter 4 Heat Textbook Questions and Answers, Notes Pdf.
Gujarat Board Textbook Solutions Class 7 Science Chapter 4 Heat
Gujarat Board Class 7 Science Heat Textbook Questions and Answers
Question 1.
State similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer:
Similarities:
- Both thermometers consist of long narrow uniform glass tubes.
- Both have a bulb at one end.
- Both contain mercury in bulb.
- Both use Celsius scale on the glass tube.
Differences:
- A clinical thermometer reads temperature 35°C to 42°C while the range of laboratory thermometer is -10°C to 110°C.
- Clinical thermometer has a kink near the bulb while there is no kink in the laboratory thermometer.
Due to kink mercury does not fall down on its own in clinical thermometer.
Question 2.
Give two examples each of conductors and insulators of heat.
Answer:
Conductors – aluminium, iron
Insulators – plastic, wood.
Question 3.
Fill in the blanks:
(a) The hotness of an object is determined by its _______.
(b) Temperature of boiling water cannot be measured by a _______ thermometer.
(c) Temperature is measured in degree _______.
(d) No medium is required for transfer of heat by the process of _______.
(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of _______.
(f) Clothes of _______ colours absorb more heat better than clothes of light colours.
Answer:
(a) temperature
(b) clinical
(c) Celsius
(d) radiation
(e) conduction
(J) dark.
Question 4.
Match the following:
| Column I | Column II |
| (i) Land breeze blows during | (a) summer |
| (ii) Sea breeze blows during | (b) winter |
| (iii) Dark coloured clothes are preferred during | (c) day |
| (iv) Light coloured clothes are preferred during | (d) night |
Answer:
| Column I | Column II |
| (i) Land breeze blows during | (d) night |
| (ii) Sea breeze blows during | (c) day |
| (iii) Dark coloured clothes are preferred during | (b) winter |
| (iv) Light coloured clothes are preferred during | (a) summer |
Question 5.
Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Answer:
More layers of clothing keep us warm in winters as they have a lot of space between them. This space gets filled up with air. Air is a bad conductor, it does not allow the body heat to escape out.
Question 6.
Look at figure. Mark where the heat is being transferred by conduction, by convection and by radiation.
Answer:
Question 7.
In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
Answer:
In places of hot climate it is advised that the outer wall of houses be painted white because white colour reflects heat and the houses do not heat up too much.
Question 8.
One litre of water at 30°C is mixed with one litre of water at 50 °C. The temperature of the mixture will be:
(a) 80°C
(b) more than 50°C but less than 80°C
(c) 20°C
(d) between 30°C and 50°C
Answer:
(d) between 30°C and 50°C.
Question 9.
An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will:
(a) flow from iron ball to water.
(b) not flow from iron ball to water or from water to iron ball.
(c) flow from water to iron ball.
(d) increase the temperature of both.
Answer:
(b) not flow from iron ball to water or from water to iron ball.
Question 10.
A wooden spoon is dipped in a cup of ice-cream. Its other end:
(a) becomes cold by the process of conduction.
(b) becomes cold by the process of convection.
(c) becomes cold by the process of radiation.
(d) does not become cold.
Answer:
(d) does not become cold.
Question 11.
Stainless steel pans are usually provided with copper bottoms. The reason for this could be that:
(a) copper bottom makes the pan more durable.
(b) such pans appear colourful.
(c) copper is a better conductor of heat than the stainless steel.
(d) copper is easier to clean than the stainless steel. –
Answer:
(c) copper is better conductor of heat than the stainless steel.
Extended Learning – Activities And Projects
Question 1.
Go to a doctor or your nearest health centre. Observe the doctor taking temperature of patients. Enquire:
(a) why she dips the thermometer in a liquid before use.
(b) why the thermometer is kept under the tongue.
(c) whether the body temperature can be measured by keeping the thermometer at some place other than the mouth.
(d) whether the temperature of different parts of the body is the same or different.
You can add more questions which come to your mind.
Answer:
(a) The doctor dips the thermometer in liquid before use to disinfect it.
(b) The thermometer is kept under the tongue because this part of body gives accurate body temperature.
(c) We can measure the temperature of the body by keeping thermometer at some place other than mouth like arm pit.
(d) The temperature of different parts of the body is not exactly same but it differs slightly.
Question 2.
Go to a veterinary doctor (a doctor who treats animals). Discuss and find out the normal temperature of domestic animals and birds.
Answer:
Normal temperature of domestic animals is 37°C to 40°C (goat) and 28°C (dog). The normal temperature of birds is about 40°C to 45°C.
Question 3.
Wrap a thin paper strip tightly around an iron rod. Try to burn the paper with candle while rotating the iron rod continuously. Does it bum? Explain your observation.
Answer:
No, the paper strip does not burn. The paper does not attain ignition temperature. The iron takes away the heat because iron is good conductor of heat.
Question 4.
Take a sheet of paper. Draw a spiral on it as shown in the Fig. Cut out the paper along the line. Suspend the paper as shown in Fig. above a lighted candle. Observe what happens. Think of an explanation.
Answer:
The paper spiral keeps moving because the hot air above the flame moves up due to convection.
Question 5.
Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of ink in one bottle. Fill this bottle with hot water. Fill the other bottle with cold water. Cover the cold water bottle with a thick piece of paper such as a postcard. Press the postcard firmly with one hand and hold the bottle with the other hand. Invert the bottle and place it on top of the hot water bottle. Hold both the bottles firmly. Ask some other person to pull the postcard. Observe what happens. Explain.
Answer:
Do it yourself