Q1. Convert the following temperatures to the Celsius scale.
(a) 293 K
To convert to Celsius:
[ °C = K – 273]
[ 293 K – 273 = 20°C]
(b) 470 K
To convert to Celsius:
[ 470 K – 273 = 197°C]
Q 2. Convert the following temperatures to the Kelvin scale.
(a) 25°C
Answer. To convert to Kelvin:
[ K = °C + 273]
[ 25°C + 273 = 298 K]
(b) 373°C
Answer. To convert to Kelvin:
[ 373°C + 273 = 646 K]
Q 3. Give reasons for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
Answer. Naphthalene turns into a gas without melting. This is called sublimation.
(b) We can get the smell of perfume sitting several meters away.
Answer. Perfume particles mix with air and move around, spreading the smell.
Q 4. Arrange the following substances in increasing order of forces of attraction between the particles—water, sugar, and oxygen.
Answer. Oxygen < Water < Sugar
(Oxygen has the weakest force, sugar has the strongest.)
5. What is the physical state of water at—
(a) 25°C
Answer.Liquid
(b) 0°C
Answer. Solid (ice) and liquid (water can exist in both states at 0°C)
(c) 100°C
Answer. Liquid and gas (water boils at 100°C, so it’s changing into gas).
6. Give two reasons to justify
(a) Water at room temperature is a liquid.
Answer. Water flows takes the shape of a container, and has a definite volume.
It doesn’t keep its shape, which is a property of liquids.
(b) An iron almirah is a solid at room temperature.
Answer. An iron almirah has a fixed shape and volume.
Its particles are tightly packed, so it is hard and doesn’t change shape.
7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer. Ice at 273 K absorbs more heat from things around it when it melts, so it cools better than water at the same temperature.
8. What produces more severe burns, boiling water or steam?
Answer. Steam produces more severe burns because it has more energy than boiling water and releases that energy when it touches your skin.