Find comprehensive BOSEM Class 7 Science solutions for the chapter Heat for the academic year 2024. Simplified explanations, solved questions, extra questions and answers and key concepts to ace your exams
Class 7 Science Textual Questions and Answers
Q1. State similarities and differences between the laboratory thermometer and the clinical thermometer.
Ans:
| Similarities | Differences |
|---|---|
| Both clinical and laboratory thermometers measure temperature. | A clinical thermometer reads temperatures from 35°C to 42°C whereas a laboratory thermometer reads temperatures generally from 10°C to 110°C. |
| Both thermometers have structural similarities having a narrow elongated tube and bulb at one end. | A Clinical thermometer measures the temperature of the human body only whereas a laboratory thermometer measures temperatures of other objects. |
Q2. Give two examples each of conductor and insulator of heat.
Ans: Conductor of heat: Iron and Copper
Insulator of heat: Plastic and wood.
Q3. 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 degrees Celsius.
d. No medium is required for the 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 colour absorb more heat than clothes of light colour.
Q4. Match the following
Ans:
| Land breeze blows during | Night |
| Sea breeze blows during | Day |
| Dark coloured clothes are preferred during | Winter |
| Light coloured clothes are preferred during | Summer |
Q5. Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Ans: Wearing more layers of clothing during winter keeps us warmer than just one thick piece of clothing because air gets trapped between the various layers. Being a poor conductor of heat, air prevents the flow of heat from our body. Hence layers of clothing keep us warmer than a thick single clothing.
Q7. In places with hot climates, it is advised that the outer walls of houses be painted white. Explain.
Ans: In places with hot climates it is advised that the outer wall of the houses to painted white because white does not absorb any heat radiation from the Sun which keeps the inside cool even if there is a hot climate outside the house.
Q8. 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.
Ans: d. Between 30 °C and 50 °C.
Q9. 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.
Ans: b. Not flow from iron ball to water or from water to iron ball.
Q10. 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
Ans: d. Does not become cold
Q11. Stainless steel pans are usually provided with copper bottoms. The reason for this could be
a. Copper bottom makes the pan more durable.
b. Such pans appear colourful.
c. Copper is a better conductor of heat than stainless steel.
d. Copper is easier to clean than stainless steel.
Ans: c. Copper is a better conductor of heat than stainless steel.
Extra questions and answers
Q1. What is a sea breeze?
Answer: A sea breeze is a gentle wind that blows from the sea toward the land, typically during the daytime. This occurs because the land heats up faster than the sea, causing the air over the land to rise and cooler air from the sea to take its place.
Q2. What is a land breeze?
Answer: A land breeze is a gentle wind that blows from the land toward the sea, usually at night. This happens because the land cools down faster than the sea, making the air over the land denser and causing it to flow towards the warmer sea.
Q3. Why do we prefer light-coloured clothes in summer and dark-coloured clothes in winter?
Answer: We prefer light-coloured clothes in summer because they reflect most of the sunlight and heat, helping to keep our bodies cool. In winter, dark-coloured clothes are preferred as they absorb more heat, helping to keep our body warm.
Q4. What are the conductors and insulators of heat? Give examples.
Answer: Conductors of heat: Materials that allow heat to pass through them easily.
Examples: Aluminium, Iron, Copper.
Insulators of heat: Materials that do not allow heat to pass through them easily.
Examples: Rubber, Plastic, Wood.
Q5. What is heat conduction?
Answer: Heat conduction is the transfer of heat through a solid material from a region of higher temperature to a region of lower temperature. For example, if you touch a metal spoon in a hot cup of tea, the heat travels from the hot end to your hand through conduction.
Q6. What is convection?
Answer: Convection is the transfer of heat in fluids (liquids and gases) through the movement of particles. For instance, when water is heated, the hot water rises, and the cooler water sinks, forming a convection current.
Q7. What is radiation?
Answer: Radiation is the transfer of heat in the form of electromagnetic waves without requiring a medium. For example, the heat from the Sun reaches the Earth through radiation.
Q8. What are the good and bad conductors of heat? Provide examples.
Answer: Good conductors of heat: Substances that transfer heat efficiently.
Examples: Metals like Silver, Copper, and Aluminium.
Bad conductors of heat (Insulators): Substances that resist heat transfer.
Examples: Wood, Plastic, Rubber.
Q9. Why does a metal spoon feel colder than a wooden spoon at room temperature?
Answer: A metal spoon feels colder than a wooden spoon at room temperature because metal is a good conductor of heat. It transfers heat away from your hand faster than wood, making it feel colder.
Q10. How does heat affect the state of matter?
Answer: Heat can change the state of matter:
Solid to Liquid (Melting): Heat energy causes solids to melt into liquids by breaking the bonds between particles.
Liquid to Gas (Evaporation): Additional heat makes the liquid particles move faster and escape as gas.
Gas to Liquid (Condensation): Removing heat causes gases to cool and condense into liquids.
Q11. Why do we wear woollen clothes in winter?
Answer: Woollen clothes are used in winter because wool traps air, which acts as an insulator. This trapped air prevents body heat from escaping, keeping us warm.
Q12. What is the difference between heat and temperature?
Answer:Heat: A form of energy that flows from a hotter object to a cooler one. It is measured in joules (J).
Temperature: A measure of the degree of hotness or coldness of an object. It is measured in degrees Celsius (°C) or Fahrenheit (°F).
Q13. Why do desert areas become very hot during the day and very cold at night?
Answer: Deserts heat up quickly during the day and cool down rapidly at night because sand has a low heat capacity. It absorbs heat quickly but also loses heat rapidly.
Q14. What is the role of heat in cooking?
Answer: Heat plays a crucial role in cooking as it breaks down the proteins, carbohydrates, and fats in food, making it easier to digest and enhancing its flavour.
