NCERT Solutions for Class 7 Science Chapter 4 Heat are provided here with simple step-by-step explanations. These solutions for Heat are extremely popular among Class 7 students for Science Heat Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 7 Science Chapter 4 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 7 Science are prepared by experts and are 100% accurate.
Page No 21:
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 wooden tile is not polished.
(c) reflects more heat than wooden tile.
(d) is a poor conductor of heat than the wooden tile.
Answer:
Marble tile is a better conductor of heat than the wooden tile, that's why it would feel cold as compared to a wooden tile on a winter morning.
Hence, the correct answer is option (a).
Page No 21:
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.
Answer:
Air trapped between the layers of newspaper is a bad conductor of heat, due to which heat would not escape from beggar's body into the surroundings that helps him to keep himself warm.
Hence, the correct answer is option (b).
Page No 21:
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 following statement is true?
(a) Paheli has a higher body temperature than Boojho.
(b) Paheli has a lower body temperature than Boojho.
(c) Both have normal body temperature.
(d) Both are suffering from fever.
Answer:
Degree celsius and fahrenheit are two scales used to measure temperature. The normal temperature of human body is 37o C which is equivalent to 98.6o F. It is the same temperature expressed in two different units. Thus, both of them have normal body temperature.
Hence, the correct answer is option (c).
Page No 21:
Question 4:
Boojho has three thermometers as shown in the given figure. He wants to measure the temperature of his body and that of boiling water. Which thermometer (s) should he choose?
 |
| (i) |
|
| (ii) |
|
| (iii) |
(a) Thermometer (i) or (iii) for measuring body temperature and (ii) for measuring the temperature of boiling water.
(b) Thermometer (i) for measuring temperature of both.
(c) Thermometer (ii) for measuring temperature of both.
(d) Thermometer (iii) for measuring temperature of both.
Answer:
Images (i) and (iii) are of clinical thermometer which is used to measure human body temperature. Image (ii) is of laboratory thermometer which can be used to measure the temperature of boiling water.
Hence, the correct answer is option (a).
Page No 22:
Question 5:
Four arrangements to measure temperature of ice in beaker with laboratory thermometer are shown in the given figure (a, b, c and d). Which one of them shows the correct arrangement for accurate measurement of temperature?
Answer:
Figure (a) shows the correct arrangement for accurate measurement of temperature.
Hence, the correct answer is option (a).
Page No 23:
Question 6:
In the given figure (a–d) shows a student reading a doctor’s thermometer. Which of the figure indicates the correct method of reading temperature?
Answer:
Figure (a) indicates the correct method of reading temperature.
Hence, the correct answer is option (a).
Page No 23:
Question 7:
In the given figure (a–d) shows the readings on four different thermometers. Indicate which of the reading shows the normal human body temperature?
Answer:
Normal human body temperature is 37o C and figure (c) shows the reading 37o C.
Hence, the correct answer is option (c).
Page No 24:
Question 8:
Shopkeepers selling ice blocks usually cover them with jute sacks. Explain why.
Answer:
Jute sacks acts as insulators, they do not allow heat to escape or enter through them. That is why, Shopkeepers selling ice blocks usually cover them with jute sacks.
Page No 24:
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 the given figure
Which of the thermometers, A or B, will show a greater rise in temperature? Give reason for your answer.
Answer:
Due to convection, hot air above the candle rises up and thus thermometers B will show a greater rise in temperature.
Page No 24:
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 reason for your answer.
Answer:
Yes, woolen cloth can be used to keep a glass of cold drink cool because wool is an insulator i.e. heat cannot enter or escape through it.
Page No 24:
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?
Answer:
Mercury expands on heating. Therefore, level of mercury rises when its bulb comes in contact with a hot object.
Page No 24:
Question 12:
A circular metal loop is heated at point O as shown in the given figure
(i) In which direction would heat flow in the loop?
(ii) 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?
Answer:
(i) Heat will flow in the loop in both the directions i.e. O to R and O to P.
(ii) At first, pins at P and R fall simultaneously, followed by the pin at Q.
Page No 25:
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.
Answer:
In case B, heat will reach pin P first, so P will fall before the pin Q. In case A, pins P and Q are equidistant from candle and heat travels in both the directions, so pins P and Q will fall simultaneously.
Page No 25:
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, setting of curd becomes difficult. Suggest a way to set curd in such a situation.
Answer:
The vessel in which curd is stored, should be wrapped with the woollen cloth or any insulator to maintain the desired temperature for setting the curd.
Page No 25:
Question 15:
You may have noticed that a few sharp jerks are given to clinical thermometer before using it. Why is it done so?
Answer:
The jerk given to the thermometer will allow mercury in or above the kink to flow into the bulb so that mercury level is below the normal temperature.
Page No 25:
Question 16:
Why is it advised not to hold the thermometer by its bulb while reading it?
Answer:
Mercury will expand due to body temperature if we hold thermometer by its bulb while reading it. That is why, it is not advised to hold the thermometer by its bulb while reading it.
Page No 25:
Question 17:
At a camp site 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 reason for your choice. Would you like to prefer the same tent during winter?
Answer:
White colour is a bad absorber and good reflector of heat, so on a hot summer afternoon tent with white fabric will be preferred.
Same colour tent will not be preferred in winter. Black colour tent is preferred during winter.
Page No 25:
Question 18:
While constructing a house in a coastal area, in which direction should the windows preferably face and why?
Answer:
While constructing a house in a coastal area windows should preferably face towards the sea because sea breeze will keep it cool during the daytime. During the day, the land gets heated faster than the water. The air over the land becomes hotter and rises up. The cooler air from the sea rushes in towards the land to take its place. The warm air from the land moves towards the sea to complete the cycle. To receive the cooler sea breeze, the windows of the houses in coastal areas are made to face the sea.
Page No 26:
Question 19:
Observe the picture given as in figure. Water is being boiled in a pan of wide base.
(i) Which position P or T will feel warmer?
(ii) Fill up the boxes P and T to indicate the mode of flow of heat to the hand.
Answer:
(i) Due to convection, hot air above the boiling water rises up and thus position P will feel warmer.
(ii) Convection
Radiation
Page No 26:
Question 20:
Look at in the given figure
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 the given figure Which pin will fall first? Explain.
Answer:
Heat will reach to pin in case A before it reaches the pin in case B, because straight length PQ is less than the curved length EDC. That is why, pin on wire in case A will fall first.
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