Question

3. A wire of 3 ohm resistance and 10cm length is stretched to 30cm length. Assuming
that it has uniform cross section what will be its new resistance ?

fast please ​

Answer 1

Solution:

Given,

Resistance of the wire = 3 Ohm

Length of the wire = 10 cm

When the wire is stretched,

New length of the wire = 30 cm

By using the formula of resistance,

R = Pl /A

Original Resistance = Pl /A

where, P means rho which is the constant of proportionally.

*Resistance is directly proportional to the length of the wire.

*Resistance is inversely proportional to the area of cross - section.

The wire is tripled of its previous length. So, it's new length is "3l" and the new cross - sectional area will be "A/3"

New resistance = 3 × Pl / A/3

New resistance = 9 × Pl / A

New resistance = 9 × R

New resistance = 9 × 3

New resistance = 27 Ohm

Thus, the new resistance will be 27 Ohm.

Answer 2

Answer:

27Ohm

Explanation:

Given

Resistance R = 3 Ohm

Length l = 10 cm

The new length l’ = 30 cm = 3 × l

R = ρ (l / A)

New resistance

Stretching length will increase and area of cross section will decrease in same order

R’ = ρ (3l / A / 3)

Hence,

R’ = 9 ρ (l / A)

R’ = 9R

R’ = 9 × 3

R’ = 27 Ohm