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## Chapter: 7th Science : Term 2 Unit 1 : Heat and Temperature

7th Science : Term 2 Unit 1 : Heat and Temperature : Book Back Questions Answers, Solution

EVALUATION

1. International unit of measuring temperature is . ______________

a. Kelvin

b. Fahrenheit

c. Celsius

d. Joule

2. In thermometer when bulb comes in contact with hot object, liquid inside it

a. expands

b. contracts

c. remains same

d. none of above

3. The body temperature of a healthy man is;

a. 0°C

b. 37°C

c. 98°C

d. 100°C

4. Mercury is often used in laboratory thermometers because it______________

a. is a harmless liquid

b. is silvery in colour and is attractive in appearance

c. Expands uniformly

d. is a low cost liquid

5. Which of the following temperature conversions is incorrect

K ( Kelvin) = °C ( Celsius) + 273.15

°C                                      K

a. -273.15                                  0

b. -123.                                 +150.15

c. + 127.                               + 400.15

d. + 450                                + 733.15

II. Fill in the blanks

1. Doctor uses clinical thermometer to measure the human body temperature.

2. At room temperature Mercury is in liquid state.

3. Heat energy transfer from hot to cold

4. -7°C temperature is less than 0°C temperature.

5. The common laboratory thermometer is a Celsius scale thermometer

III. Match the following

i. Clinical thermometer                      -      A form of energy

ii. Normal temperature human body    -     100°C of

iii. Heat                                              -       37°C

iv. Boiling point of water                   -       0°C

v. Melting point of water                    -       Kink

i) Clinical thermometer  - Kink

ii) Normal temperature of human body - 37°C

iii) Heat  -  A form of energy

iv) Boiling point of water - 100°C

v) Melting point of water  - 0°C

1. Temperature of Srinagar (J&K) is 4°C and in Kodaikanal is 3°C which of them has greater temperature ? What is the difference between the temperatures of these two places?

Kodaikanal has a higher temperature than Srinagar. The temperature difference is 7°C.

2. Jyothi was prepared to measure the temperature of hot water with a clinical thermometer. Is it right or wrong? Why?

A clinical thermometer can be used only to measure body temperature. It is scaled from 35°C to 42°C only. So it cannot be used to measure the temperature of hot water because the temperature of hot water will exceed 42°C. It is wrong to make such an attempt because the greater expansion of mercury will cause the bulb to break.

3. A clinical thermometer is not used to measure the temperature of air, why?

A clinical thermometer is scaled from 35°C to 42°C only. Its bulb should be completely covered by the part of the body such as a patient's armpit or under the tongue. So it cannot be used to measure the temperature of air.

4. What is the use of kink in clinical thermometer?

The kink prevents the mercury from flowing back into the bulb when the thermometer is taken out of the patient's mouth. Therefore we can measure the temperature conveniently.

5. Why do we jerk a clinical thermometer before we measure the body temperature?

The mercury level in a clinical thermometer will remain in the same high level even when it is taken out of the patient's mouth. So we jerk the clinical thermometer to bring the level of mercury down.

1. Why do we use Mercury in thermometers? Can water be used instead of mercury? What are the problems in using it?

1. The expansion of mercury is uniform.

2. Mercury is opaque and shining.

3. Mercury does not stick to the side of the glass.

4. It is a good conductor of heat.

5. As it has highest boiling point and a low melting point a wide range of temperatures can be measured using mercury.

6. Mercury remains in liquid form.

7. Even a small change in temperature causes visible expansion in it.

Water cannot be used in a thermometer. The Relative Density of mercury is 13.6 where as the R.D of water is just 1. So if we use water in a thermometer the length of the thermometer tube should be 13.6 times longer. It is not practicable. So we cannot use water in a thermometer.

2. Swathi kept a laboratory thermometer in hot water for some time and took it out to read the temperature. Ramani said it was a wrong way of measuring temperature. Do you agree with Ramani? Explain your answer.

Yes, I agree with Ramani. The laboratory thermometer has no kink in it. So when we take it out of the hot water the mercury level will drop down immediately. So the laboratory thermometer should not be taken out of the hot liquid while we note the reading.

3. The body temperature of Srinath is 99°F. Is he suffering from fever? If so, why?

No, Srinath doesn't have a fever. The normal body temperature is 98.6°F. Srinath's body temperature is just 99°F. This slight difference cannot be considered as fever because body temperature varies slightly from person to person.

1. Draw the diagram of a clinical thermometer and label its parts.

A clinical thermometer is a glass tube with a capillary tube at the centre. It is connected to a bulb with mercury. Mercury can rise or fall along the graduated capillary tube. All clinical thermometers have a kink that prevents the mercury from flowing back into the bulb when the thermometer is taken out of the patient's mouth, so that the temperature can be noted conveniently. There are temperature scales on either side of the mercury thread, one in Celsius scale and the other in Fahrenheit scale. Since the Fahrenheit scale is more sensitive than the Celsius scale, body temperature is measured in °F only. A clinical thermometer indicates temperatures from a minimum of 35°C or 94°F to a maximum of 42°C or 108°F.

2. State the similarities and differences between the laboratory thermometer and the clinical thermometer.

Difference between clinical and laboratory thermometer

Both the thermometers have a bulb and a stem. Mercury is used in both of them. These are the similarities. The differences are tabulated below.

Clinical Thermometer

1. It is used for taking the body temperature.

2. Clinical thermometer is scaled from 35°C to 42°C or from 94°F to 108°F.

3. Mercury level does not fall on its own, as there is a kink near the bulb to prevent the fall of mercury level.

4. Temperature can be read after removing the thermometer from armpit or mouth.

5. To lower the mercury level jerks are given.

Laboratory Thermometer

1. It is used to take temperature in laboratory.

2. Laboratory thermometer is generally scaled from -10°C to 110°C.

3. Mercury level falls on its own as no kink is present.

4. Temperature is read while keeping the thermometer in the source of temperature, e.g. a liquid or any other thing.

5. No need to give jerk to lower the mercury level.

VII. Higher Order Thinking questions

1. What must be the temperature in Fahrenheit, so that it will be twice its value in Celsius?

-24.61°F temperature is the Fahrenheit scale reading equal to twice that of the Celsius value.

2. Go to a veterinary doctor (a doctor who treats animals). Discuss and find out the normal temperature of domestic animals and birds.

The normal temperature of birds and animals are given below:

Birds have higher body temperature and much higher metabolism than human beings. So, normal body temperature of birds are 40 degree Celsius or 105 degree Fahrenheit which varies in different species of birds.

Body temperatures of domestic animals such as Cattle, Buffalo, Cow, Sheep, Goat, Donkey, Horse, Pig, Dog and Chicken falls in the range of 38 to 42 degree Celsius (or 100.4 to 107.6 degree Fahrenheit).

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