Correct Answer - Option 1 : 80 W filament is thicker
The correct answer is option 1) i.e. 80 W filament is thicker
CONCEPT:
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Power: The rate of work done by an electric current is called power. It is denoted by P. The SI unit of power is the watt (W).
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Power dissipation is given by:
\(\Rightarrow P = VI = V.\frac{V}{R} = \frac{V^2}{R}\)
Where V is the potential difference across resistance, I is current flowing and R is resistance.
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The resistivity of a material is defined as the resistance offered by a material of unit cross-sectional area and unit length.
- It is represented as
\(\Rightarrow ρ = \frac{RA}{l}\)
Where R is the resistance,l is the length of the material and A is the area of cross-section.
- Resistivity is an intrinsic property i.e. it is the same for a given type of material.
EXPLANATION:
We know, \(P =\frac{V^2}{R}\) and \(ρ = \frac{RA}{l}\)
⇒ \(P =\frac{V^2A}{ρ l}\)
Assuming that both the bulb filaments are made of the same material, their resistivities (ρ) are the same.
If connected in the same circuit, the voltage drop V across the bulbs also remains the same.
Given that the length (l) of the filaments are the same ⇒ P ∝ A
- Therefore, power directly depends on the cross-sectional area of the filament. The cross-sectional area corresponds to the thickness of the filament.
- The greater the power dissipated, the greater the thickness of the filament. Thus, 80 W filament is thicker.
