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Q1. Power links work and:
Power is defined as the rate of doing work, so it links work and time. Power = Work / Time. It tells us how quickly work is done.
Q2. 1 kW h is equal to:
1 kW h = 1000 W × 3600 s = 3,600,000 J = 3.6 × 10⁶ J. This is the commercial unit of energy.
Q3. Average power is useful when:
When power varies over time, we use average power to describe the overall rate of doing work. Average power = Total work / Total time.
Q4. Two children climbing to the same height do the same work because:
Work done in climbing = mgh. If both children have the same weight (mg) and climb the same height (h), they do the same work regardless of time taken.
Q5. Power is defined as:
Power is the rate of doing work. It is calculated by dividing the work done by the time taken. P = W/t.
Q6. One watt is equal to:
One watt is the power when 1 joule of work is done in 1 second. 1 W = 1 J/s.
Q7. Power is the rate of:
Power is defined as the rate of doing work or the rate of energy transfer. It measures how quickly work is done.
Q8. When power varies with time, we use the concept of:
When power changes over time, average power is used. It is the total work done divided by the total time taken.
Q9. Power expended in climbing depends on:
Power in climbing = Work/Time = mgh/t. So it depends on weight (mg), height (h), and time (t) taken.
Q10. Commercial electricity meters measure energy in:
Commercial electricity meters measure energy in ‘units’, where 1 unit = 1 kilowatt hour (kWh). This is used for billing purposes.
Q11. One kilowatt is equal to:
Kilowatt means 1000 watts. 1 kW = 1000 W.
Q12. Larger values of power are expressed in:
Larger power values are expressed in kilowatts (kW) or megawatts (MW). 1 kW = 1000 W.
Q13. Two girls climbing to the same height but in different times show difference in:
If two girls climb to the same height, they do the same work. The difference is in the time taken, which means their power is different (Power = Work/Time).
Q14. The SI unit of power is:
The SI unit of power is the watt (W), named after James Watt. 1 W = 1 J/s.
Q15. James Watt lived during:
James Watt, the Scottish engineer after whom the unit of power is named, lived from 1736 to 1819. He made significant improvements to the steam engine.
Q16. Power of 375 W means:
375 W means 375 joules of work is done in 1 second. Power = Energy/Time, so 375 W = 375 J/s.
Q17. One kilowatt hour is the energy used when power of 1 kW is used for:
1 kilowatt hour (kWh) is the energy consumed when a device of power 1 kW is used for 1 hour. Energy = Power × Time.
Q18. The formula for power is:
Power is calculated as work divided by time. P = W/t.
Q19. A girl expending 160 W of power is:
Power is the rate of doing work. A girl with 160 W power is doing work at the rate of 160 J per second, meaning she is doing work faster.
Q20. Joule is a unit of:
Joule is the SI unit of energy and work. It is not a unit of power (which is watt), force (newton), or time (second).
Q21. Girl A takes less time than girl B to climb the same height, so girl A has:
Since Work is the same (same weight and height), Power = Work/Time. Less time means more power. So girl A has more power.
Q22. Power compares machines based on:
Power compares how quickly different machines do work. For the same work, a more powerful machine takes less time.
Q23. If two people do the same work but one takes less time, that person has:
Since Power = Work/Time, if work is the same and time is less, power is more. The person who takes less time has more power.
Q24. Power is also defined as the rate of:
Power is the rate of doing work or the rate of transfer of energy. It measures how quickly energy is transferred.
Q25. Power measures how:
Power measures the speed at which work is done. High power means work is done quickly; low power means work is done slowly.
Q26. If two machines do the same work, the more powerful one:
For the same work, a more powerful machine completes it in less time because Power = Work/Time.
Q27. One kilowatt is equal to:
1 kW = 1000 W = 1000 J/s = 1000 J s⁻¹. This is the rate of energy transfer.
Q28. A boy running upstairs does work against:
When climbing stairs, the boy works against gravity by lifting his body weight upward. The work done is against the gravitational force.
Q29. The commercial unit of electrical energy is:
The commercial unit of electrical energy is the kilowatt hour (kWh). It is used by electricity companies for billing.
Q30. When the same work is done in different times, the rate of doing work is called:
Power is the rate of doing work. When the same work is done in different times, the power differs. Power = Work/Time.
Q31. Electrical energy used at home is measured in:
Electrical energy at home is measured in ‘units’ (kilowatt hours) by electricity meters. One unit = 1 kWh.
Q32. An agent has power of 1 W if it does:
1 W = 1 J/s. An agent has power of 1 watt if it does 1 joule of work in 1 second.
Q33. One kilowatt hour is equal to:
1 kWh = 1 kW × 1 hour = 1000 W × 3600 s = 3.6 × 10⁶ J.
Q34. Joule is too small to measure:
The joule is a small unit. For larger quantities of energy, we use larger units like kilojoule (kJ) or kilowatt hour (kWh).
Q35. The unit watt is named after:
The SI unit of power, the watt (W), is named after James Watt, the Scottish engineer who improved the steam engine.
Q36. Power tells us how:
Power measures the rate at which energy is transferred or work is done. It tells us how quickly energy is used or transferred.
Q37. A lamp consuming 1000 J in 10 s has power:
Power = Energy/Time = 1000 J / 10 s = 100 W.
Q38. A more powerful machine completes work:
A more powerful machine does the same work in less time because Power = Work/Time. Higher power means shorter time for the same work.
Q39. The unit watt represents:
The watt is the unit of power, which is the rate of doing work or rate of energy transfer. 1 W = 1 J/s.
Q40. Machines are classified based on:
Machines are classified by their power, which is the speed at which they do work or transfer energy. A more powerful machine transfers energy faster.
Q41. Increasing time while keeping work constant will:
Since Power = Work/Time, if work is constant and time increases, power decreases. They are inversely proportional.
Q42. Power of an agent may vary with:
Power can vary with time if the rate of doing work changes. For example, a person may have different power at different moments during an activity.
Q43. The work done in climbing is equal to:
Work done in climbing a height h is mgh, where m is mass and g is acceleration due to gravity. This work is stored as potential energy.
Q44. Average power is obtained by dividing:
Average power = Total work done / Total time taken = Total energy transferred / Total time.
Q45. If work done is same and time is doubled, power becomes:
Power = Work/Time. If work is constant and time is doubled, power becomes half. P’ = W/(2t) = P/2.
Q46. Power is zero when:
If no work is done (W = 0), then Power = 0/t = 0. Power is zero when there is no energy transfer.
Q47. Kilowatt hour is a unit of:
Kilowatt hour is a unit of energy, not power. It is the energy consumed when 1 kW of power is used for 1 hour.
Q48. The power of the boy climbing stairs depends on:
Power = Work/Time = mgh/t. It depends on mass (mg), height climbed (h), and time taken (t).
Q49. Power can be expressed as:
Power is expressed as J/s or J s⁻¹ (joules per second). This is equivalent to watt (W).
Q50. One ‘unit’ of electrical energy means:
One ‘unit’ of electrical energy is 1 kilowatt hour (kWh). This is the standard unit used in electricity bills.