CBSE Class 7 Science Advanced Physics Measurements Very Short Answer Questions Set 01

Very Short Answer Questions

Question 1. 10 g of water occupies ___________ cm³ of volume.
Answer:
10
In simple words: The density of water is 1 g cm⁻³, so volume = 10 g ÷ 1 g cm⁻³ = 10 cm³.

Teacher's Note:
1. Water is the standard: 1 g occupies 1 cm³.
2. Use volume = mass ÷ density for any other liquid.

Question 2. The mass of a body does not change with change in _________.
Answer:
place and time
In simple words: Mass is the amount of matter, so it stays the same everywhere.

Teacher's Note:
1. Mass is constant; weight is not.
2. Moving a body to the moon changes its weight but not its mass.

Question 3. The CGS unit of pressure is ___________.
Answer:
dyne cm⁻² (or gwt cm⁻²)
In simple words: Pressure is force per area, and in CGS the force unit is the dyne and the area unit is cm².

Teacher's Note:
1. Replace the SI units N and m² by dyne and cm².
2. The SI unit is N m⁻².

Question 4. As the temperature of a gas decreases, its density __________.
Answer:
increases
In simple words: Cooling shrinks the gas, so the same mass sits in a smaller volume.

Teacher's Note:
1. Density = mass ÷ volume.
2. Volume decreases on cooling, so density increases.

Question 5. The smallest length that can be accurately measured by using a metre scale is _____ cm.
Answer:
0.1
In simple words: A metre scale is marked in millimetres, and 1 mm = 0.1 cm.

Teacher's Note:
1. Least count is the smallest division on a scale.
2. 1 mm = 0.1 cm.

Question 6. The density of water is _____ than the density of cooking oil.
Answer:
greater
In simple words: Oil floats on water, which shows that oil is lighter for the same volume.

Teacher's Note:
1. Anything that floats on water is less dense than water.
2. The density of oil is about 0.9 g cm⁻³.

Question 7. The weight of a body varies according to the variation in the ___________.
Answer:
value of g (acceleration due to gravity)
In simple words: Weight = mg, and g changes from place to place.

Teacher's Note:
1. Weight W = mg.
2. g is smaller on the moon, so weight is smaller there.

Question 8. The CGS unit of volume is __________.
Answer:
cm³
In simple words: Volume is length × length × length, and in CGS the length unit is the cm.

Teacher's Note:
1. SI unit is m³.
2. 1 m³ = 10⁶ cm³.

Question 9. The density of a body is 500 kg m⁻³. Then its equivalent value in the CGS system is _____.
Answer:
0.5 g cm⁻³
In simple words: Divide by 1000 to change kg m⁻³ into g cm⁻³: 500 ÷ 1000 = 0.5.

Teacher's Note:
1. 500 kg m⁻³ = 500000 g ÷ 10⁶ cm³ = 0.5 g cm⁻³.
2. The body would float on water.

Question 10. The area of a square plot is 100 m². Then the value of its perimeter is _________ m.
Answer:
40
In simple words: Side = √100 = 10 m, so perimeter = 4 × 10 = 40 m.

Teacher's Note:
1. Take the square root of the area to get the side.
2. Perimeter of a square = 4 × side.

Question 11. Match the entries given in Column A with the appropriate ones in Column B (Part 1).
A. Science, B. The volume of cube of side 'S', C. CGS unit of temperature, D. Density of liquid, E. Weight, F. Liquids heat up, G. The difference in densities of substances
a. Gravitational pull by Earth, b. Due to convection current, c. The atoms packed within the substance, d. Latin word 'Scire', e. S³, f. Mass of liquid of volume V ÷ Mass of water of same volume V, g. Degree centigrade (°C)
Answer:
A – d, B – e, C – g, D – f, E – a, F – b, G – c
In simple words: Science comes from 'scire'; a cube of side S has volume S³; temperature in CGS is °C; the density of a liquid compared with water is its relative density; weight is the pull of the earth; liquids heat by convection; densities differ because atoms are packed differently.

Teacher's Note:
1. Match the easy ones first (A–d, B–e, C–g).
2. Cross off each letter as you use it.

Question 12. Match the entries given in Column A with the appropriate ones in Column B (Part 2).
A. 1 g cm⁻³, B. Convection current, C. Volume, D. Triangulation method, E. Mass, F. Density
a. 1000 kg m⁻³, b. cm³, c. Measurement of large distances, d. Mass ÷ volume, e. Change in density, f. kg
Answer:
A – a, B – e, C – b, D – c, E – f, F – d
In simple words: 1 g cm⁻³ is 1000 kg m⁻³; convection comes from change in density; volume is in cm³; triangulation measures large distances; mass is in kg; density is mass divided by volume.

Teacher's Note:
1. Match each term with its unit or meaning.
2. Check that every letter in Column B is used once.

Question 13. Match the entries given in Column A with the appropriate ones in Column B (Part 3).
A. Physics, B. X-rays, C. Aim of science, D. The volume of 1 m³ is, E. 1 dyne, F. Ventilation in a room, G. The distance between the moon and the Earth
a. To detect fracture in a bone, b. 1000 litres, c. Weight of body of mass 10⁻³ g, d. Triangulation method, e. Convection current in air, f. Deals with interaction between matter and energy, g. To find cause of an event
Answer:
A – f, B – a, C – g, D – b, E – c, F – e, G – d
In simple words: Physics deals with matter and energy; X-rays show bone fractures; science aims to find the cause of an event; 1 m³ is 1000 litres; 1 dyne is the weight of 10⁻³ g (about 1 mg); ventilation uses convection; triangulation measures the Earth–Moon distance.

Teacher's Note:
1. 1 dyne is about the weight of 1 mg, since 1 gf = 980 dyne.
2. Large distances such as the Earth–Moon distance use triangulation.

Question 14. What is the meaning of the word science?
Answer:
The word science means 'to know'. It comes from the Latin word 'scire'.
In simple words: Science is the study of how to know the unknown.

Teacher's Note:
1. Remember the Latin word 'scire'.
2. Science finds the cause of an event.

Question 15. Express the density 2 g cm⁻³ in SI system.
Answer:
To change g cm⁻³ into kg m⁻³, multiply by 1000.
2 g cm⁻³ = 2 × 1000 = 2000 kg m⁻³.
In simple words: Multiply by 1000 to go from CGS to SI.

Teacher's Note:
1. 1 g cm⁻³ = 1000 kg m⁻³.
2. Check: water is 1 g cm⁻³ = 1000 kg m⁻³.

Question 16. How does the density of a solid change with minor changes in temperature?
Answer:
It does not change (the change is negligible), because the expansion of a solid on heating is very small, so its volume remains almost constant.
In simple words: A solid hardly expands, so its density stays about the same.

Teacher's Note:
1. Density d = m/V; m and V are nearly constant for solids.
2. Liquids and gases expand much more.

Question 17. Name the device used to measure the volume of an irregular solid.
Answer:
A measuring cylinder (measuring jar).
In simple words: Dip the solid in water in the cylinder and read the rise in level.

Teacher's Note:
1. Volume = final reading − initial reading.
2. A density bottle is for liquids.

Question 18. How is the volume of a regular solid determined?
Answer:
The volume of a regular solid is found by applying the formula for its shape.
For example, cuboid = length × breadth × height, cube = (side)³, cylinder = πr²h and sphere = \( \frac{4}{3} \pi r^3 \).
In simple words: Measure the sides and use the formula.

Teacher's Note:
1. Learn the volume formulas of cube, cuboid, cylinder and sphere.
2. Keep all lengths in the same unit.

Question 19. What is the consequence of change in density of liquids with temperature?
Answer:
When a liquid is heated, the hot liquid at the bottom becomes less dense and rises while the cold, denser liquid sinks. This sets up a convection current, and the liquid heats up.
In simple words: Hot liquid rises, cold liquid sinks, and the whole liquid warms.

Teacher's Note:
1. This is why water in a pan heats evenly.
2. The same idea works for gases.

Question 20. Name the method used to measure the distance between stars.
Answer:
The triangulation method.
In simple words: A triangle is built on the sky and the distance is worked out from the scale.

Teacher's Note:
1. Tapes cannot reach stars, so triangles are used.
2. The same method gives the width of a river.

Question 21. Define one kilogram weight.
Answer:
One kilogram weight (kgwt or kgf) is the force exerted by the earth on a body of mass 1 kg. It is about 9.8 N.
In simple words: It is the pull of the earth on a 1 kg mass.

Teacher's Note:
1. It is a gravitational unit of force.
2. 1 kgf ≈ 9.8 N.

Question 22. Define one gram force.
Answer:
One gram force (gf) is the force exerted by the earth on a body of mass 1 gram. It is about 980 dyne.
In simple words: It is the pull of the earth on a 1 g mass.

Teacher's Note:
1. 1 kgf = 1000 gf.
2. 1 gf ≈ 980 dyne.

Question 23. Will the mass of a solid body change with a change in its volume?
Answer:
No. Mass is the amount of matter in the body. When the volume changes, for example by expansion on heating, no matter is added or removed, so the mass stays the same. Only the density changes.
In simple words: Expanding or shrinking does not add or remove matter.

Teacher's Note:
1. Mass changes only if matter is added or taken away.
2. Cutting a piece off a body does change its mass.

Question 24. What is a convection current? When is it formed?
Answer:
A convection current is the flow of a liquid or gas in which the hot, lighter part rises and the cold, denser part sinks. It is formed when a liquid or gas is heated.
In simple words: Hot fluid goes up, cold fluid comes down, and this keeps going in a loop.

Teacher's Note:
1. Convection happens only in liquids and gases.
2. Sea and land breezes are convection currents.

Question 25. What are the common multiple and submultiple units of mass? Express them in terms of kg.
Answer:
Multiple units: 1 quintal = 100 kg and 1 metric tonne = 1000 kg.
Submultiple units: 1 gram = 1/1000 kg and 1 milligram = 1/1000 g = 1/10,00,000 kg.
In simple words: Quintal and tonne are bigger than the kg; gram and milligram are smaller.

Teacher's Note:
1. 1 tonne = 10 quintal.
2. 1 kg = 1000 g = 10,00,000 mg.

Question 26. Write CGS units of area, force, temperature and heat.
Answer:
Area: cm²
Force: dyne
Temperature: degree centigrade (°C)
Heat: calorie
In simple words: CGS means centimetre, gram, second, so units are built from those.

Teacher's Note:
1. Heat is energy, and the CGS unit of energy is the erg; heat is also measured in calorie.
2. The SI units are m², N, K and J.

Question 27. What are the main branches of physical sciences?
Answer:
Physics and chemistry are the two main branches of physical sciences, which study inanimate objects.
In simple words: Physics studies matter and energy; chemistry studies changes in substances.

Teacher's Note:
1. Physical science deals with non-living things.
2. Biology is a life science.

Question 28. Name the steps through which science is applied.
Answer:
The steps are aim, observation, measurement, systematization and inference.
In simple words: Choose what to find, look, measure, arrange the data, then conclude.

Teacher's Note:
1. Learn the order with the first letters A, O, M, S, I.
2. Each step is explained in the notes.

Question 29. What causes the formation of the land and sea breezes?
Answer:
Land and sea heat up at different rates, so the air above them gets different densities. This sets up convection currents in the air, which we feel as land and sea breezes.
In simple words: Warm air rises and cool air rushes in to take its place.

Teacher's Note:
1. The cause is a change in the density of air with temperature.
2. By day the wind blows from sea to land.

Question 30. How does the weight of a body change with the change in altitude?
Answer:
The weight of a body decreases as the altitude increases, because the acceleration due to gravity (g) decreases with altitude. Its mass stays the same.
In simple words: Higher up, the earth pulls a little less.

Teacher's Note:
1. Weight W = mg.
2. Mass does not change with altitude.

Question 31. Convert 1 m s⁻² into cm s⁻².
Answer:
1 m = 100 cm.
So 1 m s⁻² = 100 cm s⁻².
In simple words: Multiply by 100 for each metre.

Teacher's Note:
1. Acceleration has only one length unit, so use 100 once.
2. 1 cm s⁻² = 0.01 m s⁻².

Question 32. Why does the density of a solid remain constant for minor changes in temperature?
Answer:
A solid expands so little on heating that its volume is almost constant, and its mass does not change. So density d = m/V is almost constant.
In simple words: Solids hardly expand, so density hardly changes.

Teacher's Note:
1. Liquids and gases show a large change.
2. For 20 °C to 40 °C the change in a solid is negligible.

Question 33. What is systematization?
Answer:
Systematization is the step in which the measured physical quantities are arranged in a specific way (for example in increasing or decreasing order) so that a conclusion, called inference, can be drawn.
In simple words: Put the numbers in order so the pattern is easy to see.

Teacher's Note:
1. It comes after measurement and before inference.
2. A table or graph is a good way to arrange data.