NCERT Class 7 Science Chapter 4 - Heat

Chapter 4 - Heat

Question and Answers
Question 1: State similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer:
Similarities
*Both are made of glass and consist of long narrow glass tube.
*At one end both of them have a bulb.
*Bulbs of both the thermometers consist of mercury
*Celsius scale is present in both the thermometer
Differences
Clinical Thermometer
*Temperature range is 35 to 42 Degree Celsius
* Used to measure human body temperature
* It has kink which prevents immediate back flow of mercury
Laboratory Thermometer
* Temperature range is -10 to 110 Degree Celsius
* Used to measure temperature in the laboratory
* It does not have a kink
 
Question 2: Give two examples each of conductors and insulators of heat.
Answer:
Conductors: Iron and Copper
Insulators: Plastic and wood
 
Question 3: Fill in the blanks :
(a) The hotness of an object is determined by its temperature.
(b) Temperature of boiling water cannot be measured by a clinical thermometer.
(c) Temperature is measured in Degree Celsius.
(d) No medium is required for transfer of heat by the process of radiation.
(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of conduction.
(f) Clothes of dark colors absorb more heat better than clothes of light colors.

Question 4: 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 during winter keeps us warmer than wearing just one thick piece of clothing because air gets trapped in-between layer. As air is a bad conductor of heat it does not allow the escape of the heat from the body.
 
Question 5: 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 walls of houses be painted white because white color reflects back most of the heat that is incident on it as white is a poor absorber of heat. This helps in keeping the house cool.
 
Question 6: 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 7: 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 8: 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 9: 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 colorful.
(c) Copper is a better conductor of heat than stainless steel.
(d) Copper is easier to clean than stainless steel.
Answer: (c) Copper is a better conductor of heat than stainless steel.