CBSE Class 7 Science Advanced Physics Measurements Very Short Answer Questions Set 02

Very Short Answer Questions

Question 1. State whether the following statement is true or false.
SI unit of volume is cubic metre.
Answer:
True. Volume is length × length × length, and in SI the length unit is the metre, so the unit of volume is m³ (cubic metre).
In simple words: Volume is measured in m³ in the SI system.

Teacher's Note:
1. The CGS unit of volume is cm³.
2. 1 m³ = 10⁶ cm³ = 1000 litres.

Question 2. State whether the following statement is true or false.
1 ml = 1000 cm³.
Answer:
False. 1 ml = 1 cm³ (1 cm³ is also called 1 cc). It is 1 litre that equals 1000 cm³.
In simple words: A millilitre is as big as one cubic centimetre; a litre is 1000 times bigger.

Teacher's Note:
1. ml is the short form of millilitre, not litre.
2. 1 litre = 1000 ml = 1000 cm³.

Question 3. State whether the following statement is true or false.
Mass of a given substance does not change with change in position or location.
Answer:
True. Mass is the amount of matter in a body. Matter does not become more or less when the body is moved, so the mass remains the same at all places.
In simple words: Move a stone anywhere, even to the moon, and its mass stays the same.

Teacher's Note:
1. Weight changes with place, because g changes.
2. Mass is measured by a physical balance.

Question 4. State whether the following statement is true or false.
SI unit of weight is newton.
Answer:
True. Weight is a force, and the SI unit of force is the newton (N).
In simple words: Weight is a pull, so it is measured in newton.

Teacher's Note:
1. The gravitational unit of weight is kgf.
2. 1 kgf is about 9.8 N.

Question 5. State whether the following statement is true or false.
Mass of a body cannot be zero.
Answer:
True. Every body contains some matter, so its mass can never be zero. Only the weight of a body can become zero.
In simple words: A real body always has some matter in it.

Teacher's Note:
1. Weight can be zero where there is no gravity.
2. Do not mix up mass and weight.

Question 6. State whether the following statement is true or false.
As the temperature of gases increases, its density also increases.
Answer:
False. A gas expands when it is heated, so its volume increases while the mass stays the same. Density = mass ÷ volume, so the density decreases.
In simple words: A heated gas spreads out, so there is less of it in each cm³.

Teacher's Note:
1. This is why hot air rises.
2. Cooling a gas increases its density.

Question 7. State whether the following statement is true or false.
kg l⁻¹ is a unit of density.
Answer:
True. Density = mass ÷ volume. Kilogram is a unit of mass and litre is a unit of volume, so kg l⁻¹ (kilogram per litre) is a unit of density. For water it is 1 kg l⁻¹.
In simple words: Any mass unit divided by a volume unit can be a unit of density.

Teacher's Note:
1. 1 kg l⁻¹ = 1 g cm⁻³ = 1000 kg m⁻³.
2. Other units are kg m⁻³, g m⁻³ and kg cm⁻³.

Question 8. State whether the following statement is true or false.
Triangulation method is used for measuring very long distances.
Answer:
True. Distances which cannot be measured with a scale or tape, such as the distance of the moon, planets and stars, or the width of a river, are measured by the triangulation method.
In simple words: A triangle is drawn to scale and the real distance is worked out from it.

Teacher's Note:
1. It works for places we cannot reach.
2. Scale = real distance ÷ drawn distance.

Question 9. State whether the following statement is true or false.
Density of kerosene is less than the density of water.
Answer:
True. The density of kerosene is about 0.8 g cm⁻³, which is less than 1 g cm⁻³ for water. This is why kerosene floats on water.
In simple words: Kerosene is lighter than water for the same volume, so it floats.

Teacher's Note:
1. Compare densities to predict floating and sinking.
2. Kerosene: 800 kg m⁻³; water: 1000 kg m⁻³.

Question 10. Fill in the blank.
The method of measuring distance by forming a ________ is called triangulation method.
Answer:
triangle
In simple words: The name triangulation comes from the triangle that is drawn.

Teacher's Note:
1. Triangulation = triangle + scale.
2. Two stations and the object form the triangle.

Question 11. Fill in the blank.
SI unit of area is __________.
Answer:
m² (square metre)
In simple words: Area is length × breadth, so its unit is a length unit squared.

Teacher's Note:
1. The CGS unit of area is cm².
2. 1 m² = 10⁴ cm².

Question 12. Fill in the blank.
SI unit of density is __________.
Answer:
kg m⁻³
In simple words: Density is mass in kg divided by volume in m³.

Teacher's Note:
1. The CGS unit is g cm⁻³.
2. 1 g cm⁻³ = 1000 kg m⁻³.

Question 13. Fill in the blank.
The weight of a body can be zero when ________ acts on it.
Answer:
no gravitational force
In simple words: Weight is the pull of gravity, so with no pull there is no weight.

Teacher's Note:
1. W = mg, so weight is zero if g = 0.
2. Mass stays the same even then.

Question 14. Fill in the blank.
The SI unit of energy is __________.
Answer:
joule (J)
In simple words: Energy is measured in joule in SI.

Teacher's Note:
1. The CGS unit of energy is erg.
2. 1 J = 10⁷ erg.

Question 15. Fill in the blank.
Mass of 1 ml water is ________ g.
Answer:
1. The density of water is 1 g cm⁻³ and 1 ml = 1 cm³, so the mass of 1 ml of water is 1 g.
In simple words: One ml of water weighs one gram.

Teacher's Note:
1. This is the reason water is used as the standard for density.
2. 1 litre of water has a mass of 1 kg.

Question 16. Fill in the blank.
________ is the force with which the earth pulls a body towards its centre.
Answer:
Weight
In simple words: The earth's pull on a body is what we call its weight.

Teacher's Note:
1. Weight = mass × g.
2. It is measured with a spring balance.

Question 17. Fill in the blank.
Density of a liquid can be measured by using ________.
Answer:
density bottle (with a physical balance)
In simple words: A density bottle always holds the same volume, so we only compare masses.

Teacher's Note:
1. It has a stopper with a capillary tube.
2. A measuring cylinder with a balance also works.

Question 18. Match the entries given in Column A with the appropriate ones in Column B (Part 1).
A. Standard measure, B. Physics, C. 1 cubic centimetre, D. The acceleration due to gravity, E. Density of liquid, F. 1 N
a. Unit, b. Mass of liquid of volume (V) ÷ mass of water of volume (V), c. Alters from place to place, d. Weight of a body of mass 0.1 kg, e. External behaviour of matter, f. 1 ml
Answer:
A – a, B – e, C – f, D – c, E – b, F – d
In simple words: A standard measure is a unit; physics deals with the external behaviour of matter; 1 cm³ is 1 ml; g changes from place to place; the density of a liquid in g cm⁻³ is its mass compared with the mass of an equal volume of water; 1 N is about the weight of 0.1 kg (with g = 10 m s⁻²).

Teacher's Note:
1. Do the easy matches (A–a, C–f) first.
2. 1 N = 1 kg m s⁻², so with g = 10 m s⁻² a mass of 0.1 kg weighs 1 N.

Question 19. Match the entries given in Column A with the appropriate ones in Column B (Part 2).
A. Physics, B. 0.1 tonne, C. Beam balance, D. 1 kg m⁻³
a. Study of properties of matter, b. Mass, c. 0.001 g cm⁻³, d. 1 quintal
Answer:
A – a, B – d, C – b, D – c
In simple words: Physics studies the properties of matter; 0.1 tonne = 100 kg = 1 quintal; a beam balance measures mass; 1 kg m⁻³ = 0.001 g cm⁻³.

Teacher's Note:
1. 1 tonne = 1000 kg and 1 quintal = 100 kg.
2. 1 g cm⁻³ = 1000 kg m⁻³, so 1 kg m⁻³ = 0.001 g cm⁻³.

Question 20. Match the entries given in Column A with the appropriate ones in Column B (Part 3).
A. The volume of stone, B. A gravitational unit of weight, C. 1/10,00,000 kg, D. Common balance, E. Density bottle, F. Height of a mountain, G. Convection current
a. kgf or kgwt, b. Mass, c. Triangulation method, d. Cold water sinks in and hot water rises up, e. Difference in volume of water before and after immersion of stone, f. 1 milligram, g. The stopper has a capillary tube
Answer:
A – e, B – a, C – f, D – b, E – g, F – c, G – d
In simple words: The volume of a stone is the rise in water level when it is immersed; kgf is a gravitational unit of weight; 1 mg = 1/10,00,000 kg; a common balance measures mass; the stopper of a density bottle has a capillary tube; mountain heights are found by triangulation; heating water gives convection currents.

Teacher's Note:
1. 1 kg = 1000 g = 10,00,000 mg.
2. Convection: hot liquid rises and cold liquid sinks.