Question

Power of bulb is 25watt.How many bulbs are connected in parallel with mains of 250 volt from 5A fuse.Give answer step by step.​

Answer 1

Given :

Power of bulb = 25 watt

Applied pd = 250V

Current flow = 5A

To Find :

No. of bulbs connected in parallel.

Solution :

❖ First of all we need to find resistance of each bulb$.$

When the bulbs are connected in parallel, the potential difference V is same across each bulb.

• P = V² / r

» P denotes power

» V denotes voltage

» r denotes resistance of bulb

By substituting the given values;

➙ 25 = (250)² / r

➙ r = 250 × 10

➙ r = 2500Ω

Now let's find equivalent resistance of the circuit.

As per ohm's law, current flow in the circuit is directly proportional to the applied potential difference. [V = I R]

• V denotes voltage
• I denotes current
• R denotes equivalent resistance

➙ 250 = 5 × R

➙ R = 250/5

➙ R = 50Ω

Let n bulbs each of resistance r are connected in parallel. Their equivalent resistance will be

➠ 1/R = 1/r + 1/r + .... + 1/r (n times)

➠ 1/R = n/r

➠ 1/50 = n/2500

➠ n = 2500/50

➠ n = 50 bulbs

Answer 2

Given :

Power of bulb = 25 watt

Applied pd = 250V

Current flow = 5A

To Find :

No. of bulbs connected in parallel.

Solution :

❖ First of all we need to find resistance of each bulb$.$

When the bulbs are connected in parallel, the potential difference V is same across each bulb.

P = V² / r

» P denotes power

» V denotes voltage

» r denotes resistance of bulb

By substituting the given values;

➙ 25 = (250)² / r

➙ r = 250 × 10

➙ r = 2500Ω

Now let's find equivalent resistance of the circuit.

As per ohm's law, current flow in the circuit is directly proportional to the applied potential difference. [V = I R]

V denotes voltage

I denotes current

R denotes equivalent resistance

➙ 250 = 5 × R

➙ R = 250/5

➙ R = 50Ω

Let n bulbs each of resistance r are connected in parallel. Their equivalent resistance will be

➠ 1/R = 1/r + 1/r + .... + 1/r (n times)

➠ 1/R = n/r

➠ 1/50 = n/2500

➠ n = 2500/50

➠ n = 50 bulbs