First slide

Electrical power

Question

Bulb B₁ has rating P₁ watt, V volt and bulb B₂has rating P₂ watt, V volt. If P₁ > P₂, then

Moderate

A

In combination-I, brightness of B₁ is less than the brightness of B₂.
B

In combination -II brightness of B₁ is more than the brightness of B₂.
C

In combination-I brightness of B₁ is same as the brightness of B₂.
D

In combination-II, brightness of B₁ is less than the brightness of B₂.

Solution

Resistances of B₁ and B₂ are given by R₁ = V²/P₁ and R₂ = V²/P₂ respectively.
In combination-I, $P_{1}^{1} = \frac{{V_{o}}^{2}}{R_{1}} and P_{2}^{1} = \frac{^{} V_{0}^{2}}{R_{2}} .$ since R₁ < R₂, we can conclude $P_{1}^{1} > P_{2}^{1}$ .
In combination-II, $P_{1}^{1} = i^{2} R_{1} and P_{2}^{1} = i^{2} {R_{2}}^{} .$ since R₁ < R₂, we can conclude $P_{1}^{1} < P_{2}^{1}$ .

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