CBSE Class 7 Science Advanced Physics Measurements MCQs Set 01

Answer: (a) 1 second

Explanation:
1. A wall clock has a second hand, and its smallest division marks 1 second.
2. A minute or an hour is a larger unit, so it is not the smallest reading.

Teacher's Note:
1. The smallest reading of an instrument is its least count.
2. For a wall clock the least count is 1 second.

Answer: (d) Both (a) and (b)

Explanation:
1. Area = length × breadth = 2 m × 5 m = 10 m².
2. 1 m² = 10000 cm², so 10 m² = 10 × 10000 = 100000 cm².
3. Both (a) and (b) give the same area, so the answer is both (a) and (b).

Teacher's Note:
1. Area changes by the square of the length conversion factor.
2. 1 m = 100 cm, so 1 m² = 100 × 100 cm².

Answer: (c) 10000 kg

Explanation:
1. Mass = density × volume = 2 × 10³ kg m⁻³ × 5 m³ = 10 × 10³ kg.
2. So the mass is 10000 kg.
3. 10000 g is only 10 kg, so (b) is wrong, and (a) is wrong too.

Teacher's Note:
1. Write mass = density × volume and keep the units together.
2. Check that the unit left over is kg.

Answer: (a) 200

Explanation:
1. One gram force (gf) is the force of gravity on a mass of 1 g.
2. So a body of weight 200 gf has a mass of 200 g.

Teacher's Note:
1. Gravitational units of weight are defined using mass.
2. 1 gf goes with 1 g, and 1 kgf goes with 1 kg.

Answer: (a) 1.56 mm

Explanation:
1. The pile has 9 coins and covers the scale from 0.5 cm to 1.9 cm, a height of 1.9 − 0.5 = 1.4 cm.
2. Thickness of one coin = 1.4 cm ÷ 9 = 0.1556 cm.
3. 0.1556 cm = 1.56 mm.

Teacher's Note:
1. Never read the pile from the 0 mark; read both ends.
2. Divide the total height by the number of coins, then change cm to mm.

Answer: (b) 1 g cm⁻³

Explanation:
1. Weight 5 kgf means a mass of 5 kg = 5000 g.
2. Volume = 5 litre = 5000 cm³.
3. Density = 5000 g ÷ 5000 cm³ = 1 g cm⁻³.

Teacher's Note:
1. Change kgf to kg and litre to cm³ first.
2. A density of 1 g cm⁻³ is the density of water.

Answer: (a) 1000 gram

Explanation:
1. Kilo means one thousand, so 1 kg = 1000 g.
2. 1000 mg is only 1 g, so (c) is wrong.

Teacher's Note:
1. Learn: 1 kg = 1000 g and 1 g = 1000 mg.
2. So 1 kg = 10,00,000 mg.

Answer: (b) physical balance

Explanation:
1. A physical (beam) balance compares the unknown mass with standard masses.
2. A spring balance measures weight, not mass.

Teacher's Note:
1. Spring balance → weight. Physical balance → mass.
2. Remember this pair for mass versus weight questions.

Answer: (b) \( \frac{1}{1000} \) g cm⁻³

Explanation:
1. 1 kg = 1000 g and 1 m³ = 10⁶ cm³.
2. 1 kg m⁻³ = 1000 g ÷ 10⁶ cm³ = 10⁻³ g cm⁻³ = \( \frac{1}{1000} \) g cm⁻³.

Teacher's Note:
1. To go from kg m⁻³ to g cm⁻³, divide by 1000.
2. To go from g cm⁻³ to kg m⁻³, multiply by 1000.

Answer: (d) 1125

Explanation:
1. Actual distance = 7.5 × 1,50,000 m = 11,25,000 m.
2. 1 km = 1000 m, so 11,25,000 m = 1125 km.

Teacher's Note:
1. Multiply the map distance by the scale first.
2. Then change metres to kilometres by dividing by 1000.

Answer: (d) 1000

Explanation:
1. 1 m³ = 100 cm × 100 cm × 100 cm = 10⁶ cm³.
2. 1 litre = 1000 cm³, so 1 m³ = 10⁶ ÷ 1000 = 1000 litre.

Teacher's Note:
1. Remember: 1 litre = 1000 cm³.
2. Then 1000 litre = 1 m³.

Answer: (d) 2 mm

Explanation:
1. Smallest division = 1 m ÷ 500 = 0.002 m.
2. 0.002 m = 2 mm.

Teacher's Note:
1. Least count = total length ÷ number of equal divisions.
2. Change to mm at the end to match the options.

Answer: (d) All the above

Explanation:
1. Pressure is force per unit area.
2. N m⁻² is the SI unit, and gwt cm⁻² and kgwt m⁻² are gravitational units.
3. All three are units of pressure.

Teacher's Note:
1. Pressure = force ÷ area, so any force unit over any area unit works.
2. The CGS unit is dyne cm⁻².

Answer: (c) The mass of a body can be zero.

Explanation:
1. Weight can be zero where there is no gravitational force, so (a) is correct.
2. Weight is greater than zero on the earth, so (b) is correct.
3. Mass is the amount of matter in a body and is never zero, so (c) is the incorrect statement.

Teacher's Note:
1. Weight depends on g and can vanish; mass cannot.
2. Option (d) is wrong because (a) is a correct statement.

Answer: (c) measuring cylinder

Explanation:
1. Lower the solid into water in a measuring cylinder.
2. The rise in water level is the volume of the solid.

Teacher's Note:
1. Use displacement of water for solids with no regular shape.
2. A density bottle is used for liquids.

Answer: (c) As the temperature of a gas increases, its density increases.

Explanation:
1. A gas expands on heating, so its volume increases and (a) is true.
2. The same mass in a larger volume gives a smaller density, so (b) is true.
3. (c) says density increases, which is false, so (c) is the incorrect statement.
4. (d) is not right, because (a) is a correct statement.

Teacher's Note:
1. Density = mass ÷ volume. Volume up with mass fixed means density down.
2. The printed answer key gives (b) for this question, which is wrong.

Answer: (c) 350 km

Explanation:
1. Distance on the map = 7 cm and the scale is 1 cm = 50 km.
2. Actual distance = 7 × 50 km = 350 km.
3. 35 km and 3500 m are not equal to 350 km.

Teacher's Note:
1. Multiply the map length by the scale.
2. Check that the unit matches the unit of the scale.

Answer: (c) BDACE

Explanation:
1. Take the cylinder (B).
2. Fill it with water and note V₁ (D).
3. Lower the tied solid in (A).
4. Note the new level V₂ (C).
5. Volume = V₂ − V₁ (E). The order is BDACE.

Teacher's Note:
1. Think of the steps as you would do them at a lab table.
2. The calculation always comes last.

Answer: (d) BCDA

Explanation:
1. Start from the definition of density (B).
2. Rearrange it to get the volume (C): V = 1 g ÷ 0.5 g cm⁻³ = 2 cm³.
3. Write the volume as length × breadth × thickness (D).
4. Solve for the thickness (A): 2 ÷ (10 × 5) = 0.04 cm. The order is BCDA.

Teacher's Note:
1. Work from what is given (density, mass) to what is asked (thickness).
2. The thickness comes last.

Answer: (b) 1

Explanation:
1. 10 cm on the atlas stands for 15000 km, so 1 cm stands for 1500 km.
2. 1500 km is therefore 1 cm on the atlas.

Teacher's Note:
1. Find how many km one cm stands for first.
2. Then divide the real distance by that number.

Answer: (a) change in temperature

Explanation:
1. Heated air becomes less dense and rises, and cooler air flows in.
2. This convection current is the breeze, and it is caused by the change in temperature.

Teacher's Note:
1. Heating changes density, and density differences cause convection.
2. Land and sea breezes are examples.

Answer: (c) density bottle

Explanation:
1. A density bottle holds a fixed volume of any liquid.
2. Weighing it empty, with water and with the liquid gives the density.

Teacher's Note:
1. A density bottle is the standard tool for liquids.
2. A measuring cylinder gives only volume.

Answer: (a) 314 cm²

Explanation:
1. Area = πr² = 3.14 × 10 × 10 = 314 cm².
2. 314 m² is a much larger area, so (b) and (d) are wrong.

Teacher's Note:
1. The unit of area follows the unit of the radius.
2. A radius in cm gives an area in cm².

Answer: (c) 0.1 m

Explanation:
1. Area = (side)², so side = √100 = 10 cm.
2. 10 cm = 0.1 m.

Teacher's Note:
1. Take the square root, then check the unit.
2. 10 cm = 0.1 m, not 1 m.

Answer: (a) 1 g cm⁻³

Explanation:
1. Water at 4 °C has a density of 1 g cm⁻³.
2. In SI units this is 1000 kg m⁻³.

Teacher's Note:
1. Learn both forms: 1 g cm⁻³ and 1000 kg m⁻³.
2. 1 kg m⁻³ is a very small density.

Answer: (d) All the above

Explanation:
1. Density = mass ÷ volume, so any mass unit over any volume unit is a unit of density.
2. kg m⁻³, g m⁻³ and kg cm⁻³ all fit.

Teacher's Note:
1. The standard ones are kg m⁻³ (SI) and g cm⁻³ (CGS).
2. Other combinations are valid but less used.

Answer: (d) All the above

Explanation:
1. Weight is a force, so newton (N) is the SI unit.
2. gf and kgf are gravitational units of force, so they measure weight too.

Teacher's Note:
1. Weight is measured in force units.
2. N, dyne, gf and kgf are all force units.

Answer: (b) 1.15 cm³

Explanation:
1. The blocks touch the scale at 0.7 cm and 2.0 cm, so the diameter is 2.0 − 0.7 = 1.3 cm.
2. Radius = 0.65 cm.
3. Volume = \( \frac{4}{3} \pi r^3 \) = \( \frac{4}{3} \) × 3.14 × (0.65)³ = 1.15 cm³.

Teacher's Note:
1. Measure the diameter between the two faces, not from the zero mark.
2. Cm³, not m³, is the unit here.

Answer: (d) 4000

Explanation:
1. To change g cm⁻³ into kg m⁻³, multiply by 1000.
2. 4 × 1000 = 4000 kg m⁻³.

Teacher's Note:
1. Multiply by 1000 to go from CGS to SI density.
2. Divide by 1000 to go back.

Answer: (a) 100

Explanation:
1. Volume = mass ÷ density = 100 g ÷ 1 g cm⁻³ = 100 cm³.

Teacher's Note:
1. Volume = mass ÷ density.
2. Keep the units in CGS to avoid conversions.

Answer: (c) 0.0314

Explanation:
1. Radius = 10 cm = 0.1 m.
2. Volume = πr²h = 3.14 × 0.1 × 0.1 × 1 = 0.0314 m³.

Teacher's Note:
1. Change cm to m before calculating.
2. Check your answer: 0.0314 m³ = 31.4 litre.

Answer: (c) 1000 l

Explanation:
1. Density of water = 1 kg per litre, so 1000 kg is 1000 litre.
2. That equals 1000 l (1 m³).

Teacher's Note:
1. 1 litre of water has a mass of 1 kg.
2. 1000 litre = 1 kilolitre = 1 m³.

Answer: (c) 10⁴

Explanation:
1. 1 hectare is the area of a square of side 100 m.
2. Area = 100 × 100 = 10⁴ m².

Teacher's Note:
1. Hectare is used for land area.
2. 1 hectare = 10,000 m².

Answer: (d) 1/1000

Explanation:
1. 1 kg m⁻³ = 1000 g ÷ 10⁶ cm³ = 10⁻³ g cm⁻³ = 1/1000 g cm⁻³.

Teacher's Note:
1. Divide by 1000 to change kg m⁻³ into g cm⁻³.
2. Try the same step on 4000 kg m⁻³ to check you get 4.

Answer: (c) 10000

Explanation:
1. 1 m = 1000 mm.
2. Number of parts = 1000 mm ÷ 0.1 mm = 10000.

Teacher's Note:
1. Number of parts = total length ÷ least count.
2. Use the same unit for both.

Answer: (b) One cm in a scale is divided into 100 equal parts.

Explanation:
1. Least counts: (a) 1 mm, (b) 0.1 mm, (c) 0.5 mm, (d) 0.2 mm.
2. The smallest least count, 0.1 mm, is in (b), so (b) is the most accurate.

Teacher's Note:
1. Smaller least count means a more accurate reading.
2. Change all four to mm before comparing.

Answer: (a) Calorie

Explanation:
1. Heat is a form of energy, and a calorie is a unit of heat energy.
2. Kelvin and degree centigrade are units of temperature.

Teacher's Note:
1. Heat and temperature are different quantities.
2. Temperature uses K or °C; heat uses calorie or joule.

Answer: (c) The mass of a body can be measured by using a spring balance.

Explanation:
1. A beam balance measures mass and a spring balance measures weight.
2. So (c), which says a spring balance measures mass, is wrong.

Teacher's Note:
1. Spring balance → weight; beam balance → mass.
2. Read all four options before choosing.

Answer: (a) EACFBDGH

Explanation:
1. Prepare the board (E), fix the tree as the target (A), and choose the two stations A and B (C).
2. Set up the board at A (F), fix the pins (B), repeat at B (D).
3. Draw the triangle and find the scale (G), then calculate the width (H).
4. The order is EACFBDGH.

Teacher's Note:
1. Preparation steps come first, drawing steps next and calculation last.
2. Compare with the steps used for the table and toy in the notes.

Answer: (a) CBDA

Explanation:
1. Name the empty bottle weight W₁ (C).
2. Name the other two weights W₃ and W₂ (B).
3. Find the oil and water weights (D).
4. Write the density as their ratio (A). Here oil = 80 g, water = 60 g, so D = 80 ÷ 60 ≈ 1.33 g cm⁻³. The order is CBDA.

Teacher's Note:
1. Define the symbols first, then subtract, then divide.
2. The final formula always comes last.