Question

Q.One lamp of 90 watt and 30 volt has to be used in a line of 120 volt. Lamp must be used with a residence-
1. 10 ohm in series
2. 20 ohm in parallel
3. 20 ohm in series
4. 10 ohm in parallel​

Answer 1

Answer:

Resistance of lamp

R1 = $v^{2}$/p = $30^{2}$/90 = 10 ohm

Current in the lamp

I = V/R1 = 30/10 = 3 Ampere

As the lamp is operated on 120V DC, then resistance becomes

R` = V`/i = 120/4 = 40 ohm

For proper glow, a resistance R is joined in series with the bulb

R ′ =R+R1

⇒R^(α) =R′ −R1  

=40−10=30Ω

Hope It HELPED