Flow of heat

Direction: Read the given experiment and answer the following question. Paper pins are stuck to a metal rod with wax and a lighted candle is kept below the rod as shown in the diagram below.

What does this experiment illustrate?

• Wax melts easily.

• The candle flame conducts heat.

• The thumbtacks expand when heated.

• Heat gets transferred from hot part of a body to cold part.

Which canned drink will remain cold the longest?

• P

• Q

• R

• Both P and Q

Four boxes made of different materials are left in the Sun for half an hour. Which one of the boxes will be the hottest after half an hour?

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A pot full of water is put to boil on the stove. Which one of the graphs below shows the correct change in temperature over time?

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A student took an iron rod and a wooden rod and wrapped each of them in a piece of paper. These were then heated as shown. It was found that the paper around the iron rod does not burn whereas the one around the wooden rod catches fire. It is because :

• Candle, in case of iron rod, is nearer to the paper

• Wood being a bad conductor of heat, takes away all the heat

• Iron being a good conductor of heat, conducts away the heat given to the paper

• Paper, in first case, is thicker.

Rohan wants to test whether a white object or a black object would heat up faster in the Sun. The given picture shows you his experiment. These thermometers were left out in the Sun for 30 minutes.

Which of the following statements is true?

• Thermometer 1 reads the same as thermometer 3.

• Thermometer 2 shows a higher temperature than thermometer 3.

• Thermometer 3 shows a higher temperature than thermometer 1.

• Thermometer 1 reads the same as thermometer 2.

A thermos flask is a household item that is used to keep things warm or cold support for a long time. What is the use of silvered wall in thermos flask?

• To reduce the flow of heat by conduction.

• To increase the temperature by convection.

• To reflect the heat back to reduce radiation.

• To prevent the glass vessel from breaking.

Which of the following statement(s) is/are in correct?

• Only (i) and (iii)

• Only (ii) and (iii)

• Only (iii)

• Only (i)

A saucepan is usually made up of two different materials, P and Q. Identify P and Q.

• P-Steel, Q-Aluminium

• P-Ebonite, Q-Plastic

• P-Steel, Q-Ebonite

• P-Wood, Q-Ebonite

In an experiment shown in figure, the water near the top of the tube starts boiling but the wax in the test tube does not melt completely. What do you conclude?

• Convection cannot occur in water.

• Water is a poor conductor of heat.

• Wax is a bad radiator of heat.

• Heat is not reaching at the bottom of the test tube as tube is made of insulator.