If one light bulb is brighter than another, what must be true about how much ene

Question

If one light bulb is brighter than another, what must be true about how much energy per unit time is being carried out of the bulb through visible electromagnetic waves? If two different light bulbs have the same current through them, but different potential differences across them, what can be said about which one will be brighter and why? (Relate your answer to question 1.) If two different light bulbs have the same potential difference across each of them, but different currents through them what can be said about which one will be brighter and why? (Relate your answer to question 1.)

Explanation / Answer

1) We know that the brightness of the light bulb depends on the energy released per unit time by th bulbs. The light bulb which dissipates more power(Energy per unit time) will release more electromagnetic radiation compare to others and the electric energy consumed by the light bulb will release in the form of electromagnetic radiation.

The energy released by the EM radiation is

E = h f { f -frequency of light released from the light bulb }

The brightness is just the number of photons per second hitting your eye that depends on the no.of photons in th electromagnetic radiation released by the light bulb.

2. We know that the light bulb brightness depends on the power dissipate by it.

P = V I { V = potential difference across the light bulb , I = current flow in the light bulb}

It is given that the current flowing through the each bulb is same so replace V by I R { V = I R }

P = I2 R { R -Resistance of the bulb , }

P = k R { k = I2 constant }

The light bulb which have the more resistance is brighter than the light bulb which have less resistance.

3) In this case the potential difference across each light bulb is same then

The power dissipated by the bulb is

P = V I { I = V / R }

P = V2 / R

P = k / R { k = V2 = constant }

The power released by the bulb is inversely proportional to the resistance.

Therefore the light bulb which has less resistance will give more brightness than the light bulb which has more resistance.

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