Sunday, April 24, 2016

Class7 living science Heat and its effect

Living science Heat and its effect questions with answer
Ratna Sagar Publication For CPS Samastipur

A. MUCUPLE-CHICE QUESTIONS: Choose the most appropriate answer.
1. Heat causes 
a. change of state. b. change of temperature. c. expansion. d. all of these Ö
2. Heat causes expansion because 
. heat occupies space.        b. of increase in the movement of molecules Ö
c. matter tries to escape from the heat. . 
d. none of the above is true—it is not yet known why heat causes expansion.
3. Which of these will expand the most on heating?        
a. gold              b. water            C. mercury        d. air Ö
4. 0 0C is the same temperature as 
a. 0 °F b. 212 "F. c. 32 °FÖ  d. 100 °F.
5. A bimetallic strip is made of metals M1 and M2. On cooling through the same temperature, M1 contracts more than M2  When the strip is heated, it will
a. bend towards M1.      b. bend towards M2.Ö    
c. not bend at all.          d. direction of bending cannot be predicted
6. A 10 °C fall in temperature is equal to                                       
a. 10°F fall in temperature. b. 18 °F fall in temperature.Ö 
c. 10 °F rise in temperature. d. 18 °F rise in temperature.
7. Temperature is measured by  measuring expansion on heating. Expansion in which of these is most commonly used?              
a. solid Ö                     b. liquid                        
c. gas                           d. none of these
8. When you touch a cold object
a. heat flows from your body to the object.Ö                
b. heat flows from the object to your body.
C. temperature flows from your body to the object.     
 d. temperature flows from the object to your bock B.
VERY.SIIORT.ANSWER QUESTIONS: Give one-word answers.
1. Heat is a form of  ----------[energy]     
2. For scientific work, the --------- temperature scale is used.[Kelvin]
3. The apparatus commonly used in the laboratory to show expansion on heating is the ring and -----apparatus. [ball]
4. A solid is heated from  00 C to 1000 C. Is volume increases from V1 to V2. It is now cooled it 0 'C. Will its volume at  00 C be  V1 or V2.                                    
Ans:  At 0 C, the volume of the solid will be V again.
5. Which of these expand the most on heating-- - solids, Liquids or gasesÖ ?
6. All solids expand by the same amount when heated through the same temperature increase True or falseÖ?
7. if overhead electric cables are being laid in summers. Should they be tightened up or left a little loose?
Ans: left a little loose
8. Which is the correct formula: F = (9/5)C + 32 Ö or, C = (5/9) + 32 
 9. Temperature is usually measured by measuring expansion in gases since gases expand the most. True or falseÖ?
10. What are the upper fixed points of the Celsius and the Fahrenheit scales?      
Ans: 1000 C and 2120 F
11. A -------------- thermometer is used to recorded body temperature. [Clinical]

C. SHORT-ANSWER QUESTIONS: Answer in a sentence or two.

1. List four effects that heat produces.

Ans:  Four effects of heat are as follows: Change in temperature, Change in State , Expansion ­and Chemical change ­ 

2. What does a bimetallic strip consist of?

Ans: A bimetallic strip consists of strips of iron and brass because brass expands more than iron on heating,

3. A steel bridge expands in summer. What precautions are taken to make sure this expansion does not damage the bridge?

Ans: one end of steel bridge is fixed and the other end is made to rest on rollers to provide enough space for expansion. This allows the bridge to expand easily without taking any damage.

4. How are temperature and hotness of a body related?

Ans: Temperature and hotness of a body are related directly therefore hotter body has higher temperature .

5. What do you mean by 'upper fixed point?

Ans: The temperature at which pure water boils at sea level is called 'upper fixed point’. it is 1000C or 212 0F

6. Why does a clinical thermometer have a kink in its stem?

Ans: When thermometer is taken out of our mouth mercury in it starts contracting and tends to flow back into the bulb. Therefore kink is provided in the stem to prevent mercury from falling back immediately into bulb.

D. LONG-ANSWER QUESTIONS: Answer in about 50 words.

1. Explain why a substance expands on heating.

Ans: When we heat a substance its molecules gain energy and start vibrating rapidly and spread out. As a result a substance expands.

3. Explain why gases expand more than liquids and solids.

Ans: Gases expands more than solid and liquid because the molecules of are held together with very weak force of attraction as compared to that of liquids and solids.

2. Give one example where expansion on heating is put to good use. Explain the working with the help of a labelled Diagram. 

Answer: In fire alarm expansion put in good use. The alarm contains two strips of iron and brass bolted together. 

When it is heated because of fire, brass expands more than iron and bends towards iron. Bell starts ringing.
Once the strip cools down, it will return to its original  position and stop the alarm. 

4. Explain with the help of a labelled diagram an experiment to show that liquids expand when heated.

Ans: Take a flask filled with coloured liquid up to its brim.

Insert a glass tube through hole in the rubber cork.

Now, fit the cork tightly on the mouth of the flask.

Note down the level of water in the glass tube. Now, start heating the flask.

At first, the liquid level will drop, but after a few moments it will start rising.

At first the liquid level will fall due to the expansion of the flask on heating.

When this heat reaches the liquid, it starts expanding. [sea diagram]

5. Expansion on heating can be a nuisance. Explain giving two examples.

Ans: (a) Railway tracks are made up of iron which expands during the summers. Hence, if no gap is left between two sections of railway tracks, they will bend and causes serious accidents

(b) A steel bridge also expands during the summers. This is the reason why one end of a steel bridge is fixed and the other rested on rollers with enough space on its front to allow it to expand easily. If this is not done, it will only cause serious damage to the bridge
6. Convert: 25 0C to 0F and 86 °F to oC   Ans :  0F =  (9/5) x 25 + 32   = 77 0
and  oC = 5/9(86 - 32) 30
7. Calculate the temperature at which the reading on the Fahrenheit scale is double the reading on the Celsius scale.
Answer: Let the reading on the Celsius scale be X, then reading on the Fahrenheit scale =  2x
 Now,  0C = 5/9(F-32) Þ  x = 5/9( 2x -32)  Þ  x= 160
Hence, when the temperature is 160 C, then on the Fahrenheit scale it will be 320 F.

8. What precautions will you take while measuring temperature with a laboratory thermometer? What extra precaution will you take while measuring body temperature with a clinical thermometer?

Precautions that should be taken while using a laboratory thermometer for measuring temperature are as follows:

  • It should be properly washed before and after use. It should be kept upright while reading the temperature. 
  • Its bulb should be properly dipped into the liquid or touched to the surface of the material. 
  • Its bulb should not touch the surface of the container in which the material or liquid has been placed. 
  • It should be handled with care, as it is made up of a glass tube.
Precautions that should be taken while using a clinical thermometer for measuring body temperature are as follows: 
  • Sterilise the thermometer using an antiseptic solution before and after its use.
  • Ensure that the mercury level is below 35 C before measuring the temperature.
  • Take the reading keeping the level of mercury along the line of sight.
  • Avoid holding it by its bulb while reading the temperature
HOTS Questions: Think and answer.           

1. You are planning to go to a very cold place where the night temperature drops to —50 °C. Which thermometer will you take with you—mercury or alcohol? Why?

Ans: To measure the temperature of cold places where the night temperature drops to ­50°C, we will use the alcohol thermometer. This is because alcohol freezes at ­115°C, while mercury freezes at ­38°C.

2. Which is greeter-- 1° rise in the Celsius scale or a 1° rise in the Fahrenheit scale?

Ans: 1° rise rise in the Celsius scale is greater than a 1° rise in the Fahrenheit scale.
F2 – F1 = = [(9/5)C2 + 35 ] -  [(9/5)C1 + 35] 
Þ 10F = (9/5)[ C2 – C1
Þ 10F = 0.56 times [ C2 – C1]
Hence, for the same temperature increase, the increase on the Celsius scale is only by 0.56 , while that on the Fahrenheit scale is by 1 .
Hence, 1 rise in the Celsius scale is greater than the 1 rise on the Fahrenheit scale.

3. Can a clinical thermometer be used to measure the temperature of boiling water? Why

Ans: A clinical thermometer has the temperature range from 35 0C to 42 0C. But the boiling point of water is 100 C. Therefore, it is not possible to measure the temperature of boiling water with a clinical thermometer.

4. Why is a laboratory thermometer not used to measure body temperature?

Ans: Laboratory thermometers do not have Kink to prevent back flow of liquid into capillary tube as soon as taken out from our mouth.

 5. You have seen that an ordinary glass tumbler can crack if very hot or very cold water is poured into it. You have two glass tumblers made of ordinary glass—one with thick walls and the other with very thin walls. Which one is more likely to crack when very hot or very cool water is poured into them?

Ans: In thin wall of glass more amount of heat passed per second as compared to thick. Thus, thin tumbler will crack first when same temp difference occurred for same time.

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