Multiple Choice Questions
Question 1: A marble tile would feel cold as compared to a wooden tile on a winter morning because the marble tile
(a) is a better conductor of heat than the wooden tile.
(b) is polished while the wooden tile is not polished.
(c) reflects more heat than wooden tile.
(d) is a poor conductor of heat than the wooden tile.
Solution 1: (a) is a better conductor of heat than the wooden tile.
As a marble tile, compared to wood, it is a strong conductor of fire. A marble tile would also allow heat to quickly flow through itself, keeping it cool on a winter morning.
Question 2: A beggar wrapped himself with a few layers of newspaper on a cold winter night. This helped him to keep himself warm because
(a) friction between the layers of newspaper produces heat.
(b) air trapped between the layers of newspaper is a bad conductor of heat.
(c) newspaper is a conductor of heat.
(d) newspaper is at a higher temperature than the temperature of the surrounding.
Solution 2: (b) air trapped between the layers of newspaper is a bad conductor of heat.
His body's heat does not leak into the climate, which would help him keep his body warm.
Question 3: Paheli and Boojho measured their body temperature. Paheli found her’s to be 98.6 °F and Boojho recorded 37°C. Which of the followng statement is true?
(a) Paheli has a higher body temperature than Boojho.
(b) Paheli has a lower body temperature than Boojho.
(c) Both have a normal body temperature.
(d) Both are suffering from fever.
Solution 3: (c) Both have normal body temperature.
Two measures for temperature determination are degrees Celsius and Fahrenheit. The normal body temperature is 37°C, equivalent to 98.6 F. Therefore, they both have a natural body temperature.
Question 4: Boojho has three thermometers as shown in Figure 4.1. He wants to measure the temperature of his body and that of boiling water.
Which thermometer (s) should he choose?
(a) Thermometer (i) or (iii) for measuring body temperature and (ii) for measuring the temperature of boiling water.
(b) Thermometer (i) for measuring the temperature of both.
(c) Thermometer (ii) for measuring the temperature of both.
(d) Thermometer (iii) for measuring the temperature of both.
Solution 4: (a) Thermometer (i) or (iii) for measuring body temperature and (ii) for measuring the temperature of boiling water.
Picture number (i) and (iii) are used to measure body temperature and are known as clinical thermometer but picture (ii) is used to record room temperature and is called as laboratory thermometer.
Question 5: Four arrangements to measure the temperature of the ice in a beaker with laboratory thermometer are shown in Figure 4.2 (a, b, c and d). Which one of them shows the correct arrangement for accurate measurement of temperature?
Solution 5: (a)
Question 6: Fig 4.3 (a–d) shows a student reading a doctor’s thermometer. Which of the figure indicates the correct method of reading temperature?
Solution 6: (a)
Question 7: Figure 4.4. (a–d) shows the readings on four different thermometers. Indicate which of the reading shows the normal human body temperature?
Solution 7: (c)
Normal body temperature of human is around 37º C which is shown in thermometer (c).
Very Short Answer Questions..................
Question 8: Shopkeepers selling ice blocks usually cover them with jute sacks. Explain why.
Solution 8: Ice block shopkeepers usually cover them with jute sacks since materials such as sawdust and newspaper jute sacks serve as insulators and can not allow heat to leave or penetrate through them.
Question 9: A laboratory thermometer A is kept 7 cm away on the side of the flame while a similar thermometer B is kept 7 cm above the flame of a candle as shown in Figure 4.5.
Which of the thermometers, A or B, will show a greater rise in temperature? Give a reason for your answer.
Solution 9: Picture (b) since, due to convection, hot air rises from the candle that burns.
Question 10: To keep her soup warm Paheli wrapped the container in which it was kept with a woollen cloth. Can she apply the same method to keep a glass of cold drink cool? Give a reason for your answer
Solution 10: Yeah, a woollen cloth should be used to hold a glass of cold drink cool, since woollen is an insulator that does not allow heat to leave or join.
Question 11: In a mercury thermometer, the level of mercury rises when its bulb comes in contact with a hot object. What is the reason for this rise in the level of mercury?
Solution 11: Mercury is expanded on heating, so when it comes in contact with a hot object, its level in the capillary increases.
Short Answer Questions...................
Question 12: A circular metal loop is heated at point O as shown in Figure 4.6.
- In which direction would heat flow in the loop?
- In which order the pins at points P,Q and R fixed with the help of wax fall if points O, P, Q and R are equidistant from each other?
Solution 12:
- The heat in the loop will flow in both the directions i.e. from O to P and from O to R.
- The pins at R and P would fall concurrently at the beginning, followed by the pins at Q.
Question 13: In the arrangements, A and B shown in Figure 4.7, pins P and Q are fixed to a metal loop and an iron rod with the help of wax. In which case are both the pins likely to fall at different times? Explain.
Solution 13: The pin P will drop before pin Q in case 'B' because the heat will first reach pin P. The heat travels in both directions in the case 'A' and pins P and Q will drop simultaneously.
Question 14: For setting curd, a small amount of curd is added to warm milk. The microbes present in the curd help in setting if the temperature of the mixture remains approximately between 35°C to 40°C. At places, where room temperature remains much below the range, the setting of curd becomes difficult. Suggest a way to set curd in such a situation.
Solution 14: Woollen or any other insulator should be wrapped in order to preserve the desired temperature container with curd. By keeping the container near the gas stove, curd can also be set in a room with a temperature below optimum.
Question 15: You may have noticed that a few sharp jerks are given to clinical thermometer before using it. Why is it done so?
Solution 15: The jerk causes mercury to leak into the lamp above the kink, allowing the amount of mercury below the usual temperature.
Question 16: Why is it advised not to hold the thermometer by its bulb while reading it?
Solution 16: The mercury would be expanded by our body temperature if we keep the thermometer by its bulb when reading it.
Question 17: At a campsite, there are tents of two shades – one made with black fabric and the other with white fabric. Which one will you prefer for resting on a hot summer afternoon? Give a reason for your choice. Would you like to prefer the same tent during winter?
Solution 17: I will choose a tent with white fabric in season, as white is a poor absorber and a strong heat reflector. But I will prefer a tent with black fabric in winter, because black is a strong absorber and a poor heat reflector.
Question 18: While constructing a house in a coastal area, in which direction should the windows preferably face and why?
Solution 18: Housing windows in coastal areas should ideally face the water, since the sea breeze makes it cool throughout the day.
Question 19: Observe the picture given in Figure 4.8. Water is being boiled in a pan of wide base.
- Which position P or T will feel warmer?
- Fill up the boxes P and T to indicate the mode of flow of heat to the hand.
Solution 19: Position 'P' will feel warmer as the hot air rises.
(P) Convection
(T) Radiation
Question 20: Look at Figure 4.9.
The length of wire PQ in case of A is equal to the diameter of the semicircle formed by the wire CDE, in case B. One pin is attached to each wire with the help of wax as shown in Figure 4.9. Which pin will fall first? Explain.
Solution 20: The pin on the wire in case A will fall first as heat will lead to it before it hits the pin in case B.