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Wave particle duality

Let n and m denote the number of photons emitted by a red and blue bulb respectively of equal power in a given time.Is n=m?

Answer:

No

The energy of a photon is hν

where ν is the frequency.

Power = energy/time

==> nhν1 = mhν2

==> nν1 = mν2

clearly n not equal to m

Power Factor

Divya asked:

“A COIL  HAS  A POWER  FACTOR OF 0.707 AT 60Hz, THEN ITS  POWER  FACTOR AT 180Hz WILL BE- ……….?

Ans:

(to be posted soon)

A Problem from power

Gayathri Shinde Asks:

“Please answer this question with explanation:

The power output of a machine that lifts a 600 kg
weight through a height of 20m in 1min is:
@)1.96kW    b)0.98kW

c)12kW      d)3.92kW”

Answer:

Use the formula power = work /time

P = \frac{mgh}{t}
[youtube=http://www.youtube.com/watch?v=BVxEEn3w688&rel=0&w=480&h=390]

 

Power factor in AC circuits

Dany Asked:

“what is meant by power factor?”

Ans:

In AC circuits, Power factor is defined as the ratio of true power to apparent power.

Power Factor =\frac{True Power}{Apparent Power}

If φ is the phase difference between E and I, then

True Power = EvIv cos φ and the Apparent Power is EvIv

Therefore,

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