Here in this post we provided NCERT Exemplar Problem Class 7 Science Heat Chapter 4 Full Explanation by group of Science Experts. We have provided here each questions answer with reason behind the answer.
Hope it help you!
Heat Class 7 Exemplar full Explanation:
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Multiple Choice Questions
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 tile.
Answer:- a) is a better conductor of heat than the wooden tile .
Wood is bad conductor of heat it is insulator . Heat will not flow Through the wooden tile . Marble tile gets cooler because it is slightly better conductor of heat than the wooden.
2.) A beggar wrapped himself a few layers of newspapers on a cold winter night. This helped him to keep himself warm because
a) Friction between the layers of newspaperproduces 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:- b) Air trapped between the layers of newspapers is a bad conductor of heat.
Newspaper is bad conductor of heat i.e it is a insulator it will not allow to flow the heat.
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:- c) both have normal body temperature.
Both are normal body temperature 98.6° F is same as that of 37°C.
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 be choose?
a) Thermometer I or III for measuring body temperature .
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:- a) temperature I or III for measuring body temperature.
For measuring body temperature I and III is suitable.
5.) For arrangements to measure temperature of ice in breaker with laboratory thermometer are shown in figure 4.2 ( a , b, c, 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.
Thermometer should be kept upright not titled.
Thermometer’s bulb should not be touched by the hand. Bulb should be free from all sides due to which the room temperature will be measured accurately.
6.) Figure 4.3 shows a student reading a doctor’s thermometer. Which of the figure indicates the correct method of reading temperature?
Answer:- figure a) shows the correct method of reading temperature.
While reading doctors Thermometer it is important to hold it firmly and note the temperature. thermometer Should not hold from the bulb is important.
7.) Figure. 4.4 (a-d) shows the reading on four different thermometers. Indicates which of the reading shows the normal human body temperature.
Answer:- c) indicates normal body temperature.
Normal temperature of human body is 37°C.
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Very Short Answer Questions
8.) Shopkeepers selling ice blocks usually cover them with jute sacks. Explain why.
Answer:- Ice is solid state of water . Water in the freezing condition is ice, if the temperature of the ice blocks goes down due to Contact with surrounding temperature. Heat flows from higher temperature to the lower temperature. Thus ice can be melt and becomes water again when get in contact with the surrounding temperature. To avoid the melting of ice an insulator should be used to cover the ice, such as jute sacks , newspaper, wood saw, or plastic which will be act like an resistance to the external heat and ice will not melt.
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 thermometer A or B , will show a greater rise in temperature ? Give reason for your answer.
Answer:-the heat from the flame of the candle will be go up more than the side of the candle. Heat goes up and the air gets heated by the convection thus the thermometer B which is kept above the flame candle will experience more heat. While on the sides of candle there is no convention therefore the thermometer A will not show rise in temperature. Thermometer B will show greater rise in temperature.
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 drinks cool? Give reason for your answer.
Answer:- As woollen cloth are poor conductors of heat it will not allow to transfer heat. As the conduction of heat will not occur from the woollen clothes the same method can be applied for keeping soup warm as well as cold drinks cool.
11.) a mercury thermometer, the level of mercury rises when it’s bulb comes in contact with a hot object. What is the reason for this rise in the level of mercury?
Answer:- thermometer is the device to measure the temperature. It consists of a shining metal known as ‘mercury’. When the bulb of the thermometer get in contact with the hot object or heat, the mercury in the thermometer expands and rises up in the capillary tube.
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Short Answer Questions
12.) A circular metal loop is heated at point O as shown in figure. 4.6
I) In Which direction would heat flow in the loop ?
Answer:- Heat will flow in both the directions as the loop is made up of metal. Metal is good conductor of heat. the conduction of heat will occur, from O to P and O to R. In both directions heat will flow .
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:- If the pins are fixed with wax on the points P, Q, R and O . The first pin will fall at the point of O because it is directly gets heat from the candle. Pins on the points P and R will fall simultaneously as the heat flows from the both sides. At the last pin at point Q will fall down.
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 the figure A) pins P and Q are fixed on the metal loop both the pins are equidistant from the point where the candle is directly heating . In the loop heat will flow from both the sides therefore both the pins will fall simultaneously.
In the figure B) Iron rod is used where the pins are kept in line therefore heat will reach at the point P and pin P will fall first than the pin Q will fall.
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:- for setting curd , the temperature needed is 35 to 40°C. if the room temperature is below the range then in that situation for setting curd we can wrap the container with an insulator . Due to which heat will be maintained. We can use woollen clothes or any poor conductor of heat substances. Or the container can be kept in the sunlight or near the gas stove for maintaining heat.
15.) You may have noticed that a few sharp jerks are given to clinical thermometer before using it . Why is it done so ?
Answer:- for measuring the temperature it is important to hold it girly and give some jerks. Due to the jerks the level of the mercury in the capillary tube will be down. It is important to ensure that it should fall below 35°C. Clinical temperature is used to measure body temperature. Normal body temperature is 37° C. When the mercury is goes below 35°C due to jerks then the accurate temperature of the body will be shown.
16.) Why is it advised not to hold the thermometer by its bulb while reading it ?
Answer:- Thermometer is used for measuring temperature . The bulb of the thermometer contains mercury which expands when get in contact with the heat and thus shows rise in temperature. If we hold with the bulb of the thermometer the mercury will rise due to our body temperature therefore it is advised not to hold the thermometer by its bulb while reading it.
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:- Black fabric tent is preferred for the winter because black fabric or dark coloured fabric absorb more heat. Due to that reason we get comfortable in the winter. While the white tent is used for the summer as light coloured clothes reflect most of the heat falls on the cloths that’s why we feel comfortable in the summer afternoon.
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, the direction of the windows should be at the side of sea. The cool breeze from the sea will flow towards the house and due to windows facing in that direction house will be keep during the day inhot afternoon.
19.) Observe the picture given as figure. 4.8 water is being boiled in a pan of wide base.
I) Which position P or T will feel warmer ?
Answer:-position P will feel more warmer than the position T. As the hot Air goes up in the direction.
II) Fill up the boxes P and T to indicate the mode of flow of heat to the hand .
Answer:- Box P → Convention
Box T → Radiation
20.) Look at the 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.
Answer:- The length of the wire in case of A and B is same but in Case A the wire is straight and semicircle in the B. The heat will reach to the pin First in the case A and it will fall down before the pin in the case B.