Samacheer Kalvi 7th Science Term 2 Unit 1 Book Back Questions and Answers:

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Science – Term 2

Unit 1 Heat and Temperature

I. Choose the correct answer:

1. International unit of measuring temperature is
(a) Kelvin
(b) Fahrenheit
(c) Celsius
(d) Joule
Answer: (a) Kelvin

2. In a thermometer when the bulb comes in contact with a hot object, the liquid inside it
(a) expands
(b) contracts
(c) remains same
(d) none of above
Answer: (a) expands

3. The body temperature of a healthy man is;
(a) 0°C
(b) 37°C
(c) 98°C
(d) 100°C
Answer: (b) 37°C

4. Mercury is often used in laboratory thermometers because it
(a) is a harmless liquid
(b) is silvery in colour and attractive in appearance
(c) Expands uniformly
(d) is a low-cost liquid
Answer: (c) Expands uniformly

5. Which of the following temperature conversions is incorrect K (Kelvin) = oc ( Celsius) + 273.15
°C               K
a.       -273.15          0
b.      -123.         +150.15
c.      + 127.       + 400.15
d.     + 450        + 733.15
Answers: (d.)  °C + 450 ,k  + 733.15

II. Fill In the blanks:

1. The doctor uses ________ thermometer to measure the human body temperature.
2. At room temperature mercury is in _______ state.
3. Heat energy transfer from _______ to _______
4. -7°C temperature is _______ than 0°C temperature.
5. The common laboratory thermometer is a _______ thermometer.

Answer:

1. clinical
2. liquid
3. hotter object, colder object
4. less
5. Mercury

III. Match the following:

1. Clinical thermometer – A form of energy
2. The normal temperature of the human body – 100°C
3. Heat – 37°C
4. The boiling point of water – o°c
5. The melting point of water – Kink

Answer:

1. Clinical thermometer – Kink
2. The normal temperature of the human body – 37°C
3. Heat – A form of energy
4. The boiling point of water – 100°C
5. Melting point of water – 0°C

IV. Give a very short answer:

1. Temperature of Srinagar (J&K) is -4°C and in Kodaikanal is 3°C which of them has a greater temperature? What is the difference between the temperatures of these two places?
Answer:
Kodaikanal has a greater temperature.
Temperature of Srinagar (J &K) = -4°C
Temperature of = 3°C
Difference = -4°C + 3°C = 7°C
Srinagar is colder than that of kodaikanal.

2. Jyothi was prepared to measure the temperature of hot water with a clinical thermometer. Is it right or wrong? Why?
Answer:
It is wrong because clinical thermometer has a small temperature range (35°C to 42°C or 94°F to 108°F). If it is used to measure the temperature of hot water, the glass will crack/ burst due to excessive pressure created by the expansion of mercury.

3. A clinical thermometer is not used to measure the temperature of the air, why?
Answer:
The range of the clinical thermometer is less than that of the thermometer used to measure the temperature of the air.

4. What is the use of kink in clinical thermometers?
Answer:
A kink is a clinical thermometer 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.

5. Why do we jerk a clinical thermometer before we measure the body temperature?
Answer:
The jerk to the thermometer will allow the mercury level to flow into the bulb so that the mercury level is below the normal temperature.

V. Give a Short Answer:

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

1. We use mercury in thermometers as they remain in liquid form even with a change temperature in it.
2. A small change in the temperature causes a change in the volume of a liquid.
3. Water cannot be used as a thermometric liquid, because it is not helpful to measure below 0°C and above 100°C.
4. Water is transparent. So it makes the reading of the scales of the thermometer more difficult, water wets the glass tube so its steady is a glass tube.
5. Due to these constraints, it is not used as a thermometric liquid.

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

1. The laboratory thermometer does not have a kink. So, when Swathi takes out the thermometer, the level can go back because of absence of a kink.
2. So Swathi should note the reading when the thermometer bulb has surrounded by hot water.

3. The body temperature of Srinath is 99°F. Is he suffering from a fever? If so, why?
Answer:
Srinath is having a fever because the normal body temperature is 98.6°F.

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