Question

(iii) Define 'Power'.​

Answer 1

Answer:

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Power:

Power is defined as rate of doing " work done " (or) " Energy " that is transferred in a time " t ".

Expression:

• Power = Work done / time.
• Power = Energy / time.

Units:

• S.I. unit = Watts (W).
• C.G.S. units = Horsepower (hp).

Dimensions:

• M L² T⁻³

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Examples:

★ Calculate the power of an electric motor that can lift 800 kg of water to store in a tank at a height of 1500 m in 20 s. ( g=10 m / s² ).

Solution:

⇒ Power = Work done / time

⇒ P = m g h / t

⇒ P = 800 × 10 × 1500 / 20

⇒ P = 8000 × 1500 / 20

⇒ P = 12000000 / 20

⇒ P = 1200000 / 2

⇒ P = 600000 W

∴ Power of Electric motor is 600000 W.

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Example:

★ A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long in time 10 seconds. How much is the Power of the plough?

Solution:

⇒ Power = Work done / time

⇒ P = F.s / t

⇒ P = 140 × 15 / 10

⇒ P = 2100 / 10

⇒ P = 2100 / 10

⇒ P = 210 / 1

⇒ P = 210 W

∴ Power of  is 210 W.

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Answer 2

$\huge\underline\red{\sf Power :-}$

★ Power is the rate of doing work or delivering energy ★

★ S.I Unit★ → S.I unit of power is Watt or joule per second (J/s) .It can be denoted by letter "w"

★CGS Unit ★ → Horsepower (hp)

★Formula★

• P = W / ∆t
• Average power = V²/R ( where v replaces the rms voltage)

Where P = Power , W = Work and ∆t = Elapsed time

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★ Power is a Scalar quantity because Power on its own is defined as being the rate of energy transfer, and it has no additional information as to its direction ★

→ How power is measured?

• The power consumption of small devices is usually measured in Watts, and the power consumption of larger devices is measured in kilowatts (kW), or 1,000 Watts.

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