Question Answers For All Chapters – General Science Class 7
Measurement of Physical Quantities-Solutions
Exercise
1. Write answers to the following questions in your own words.
(a) Why is the weight of the same object different on different planets?
→ Weight depends on gravity, and each planet has different gravitational force. For example, the Moon’s gravity is weaker than Earth’s, so objects weigh less on the Moon.
(b) What precautions will you take to make accurate measurements in day-to-day affairs?
→ We should use proper measuring devices, check for zero error, take readings at eye level, and ensure the balance is stable while weighing.
(c) What is the difference between mass and weight?
| Mass | Weight |
|---|---|
| Amount of matter in an object | Gravitational force acting on an object |
| Measured in kg (kilograms) | Measured in N (Newtons) |
| Remains constant everywhere | Changes with gravity |
| Scalar quantity | Vector quantity |
2. Who is my companion? (Match the following)
| Group A | Group B |
|---|---|
| (1) Velocity | (c) Metre/second |
| (2) Area | (e) Square metre |
| (3) Volume | (a) Litre |
| (4) Mass | (b) Kilogram |
| (5) Density | (d) Kilogram/cubic metre |
3. Explain giving examples.
(a) Scalar quantity
→ A scalar quantity has only magnitude (size) but no direction.
Example: Mass (5 kg), Temperature (30°C).
(b) Vector quantity
→ A vector quantity has both magnitude and direction.
Example: A car moving 60 km/hr north, Force acting downward due to gravity.
4. Explain, giving examples, the errors that occur while making measurements.
(a) Instrument Error → If a damaged or faulty scale is used, measurements may be incorrect.
(b) Parallax Error → If a person sees the scale from a wrong angle, the reading may be wrong.
(c) Zero Error → If a measuring tool does not start at exact zero, all readings will be incorrect.
5. Give reasons.
(a) It is not proper to measure quantities by using body parts as units.
→ Different people have different hand spans, feet sizes, and arm lengths, so the measurements will not be uniform or accurate.
(b) It is necessary to get the weights and measures standardized at regular intervals.
→ Standardization ensures that shopkeepers, industries, and scientists use the same accurate units, preventing fraud and errors.
6. Explain the need for accurate measurement and the devices to be used for that.
Accurate measurement is necessary in medicine, construction, science, and daily life to avoid errors.
Devices used:
- Weight → Electronic or beam balance.
- Length → Scale, measuring tape.
- Time → Stopwatch, clock.
- Temperature → Thermometer.
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