Question

You have 2 electric lamps having rating 40W; 220V and 60W ; 220V. Which of the two has a higher resistance? Give reasons for your answer. If these two lamps are connected to a source of 220V, which will glow brighter?

Answer 1

Explanation:

Power of first lamp, P₁ = 40 W

Power of other lamp, P₂ = 60 W

Voltage of first lamp, V₁ = 220 V

Voltage of other lamp, V₂ = 220 V

Power of an electrical appliances is equal to :

$P=\dfrac{V^2}{R}$

For first lamp :

$R_1=\dfrac{V_1^2}{P_1}$

$R_1=\dfrac{(220\ V)^2}{40\ W}$

$R_1=1210\ ohms$

For second lamp :

$R_2=\dfrac{V_2^2}{P_2}$

$R_2=\dfrac{(220\ V)^2}{60\ W}$

$R_2=806.6\ ohms$

So, the resistance of first lamp is high

The function of resistance is to oppose the flow of electric current. If these two lamps are connected to a source of 220 V, then the lamp having less resistance will glow brighter i.e. lamp 2

Answer 2

P=V^2/R

R=V^2/P

R1=220^2/60=80.67ohm

R2=220^2/40=1210ohm

R=(806.67×1210)/(806.67+1210)

= 484ohm

I = 220/484

= 0.45 A

Hence, current drawn from 220V is 0.45A.

Hence, The resistance of first lamp if high.

Hence, The lamp having less resistance will glow brighter, that is lamp 2.