TG EAMCET 4 May 2025 Shift 1 Paper

We use the formula:
‌

r

R

=‌

l1−l2

l2

where r is internal resistance, R is the external resistance, l1 is the first balancing length, and l2 is the new balancing length when R is connected.
Since the balancing length decreases by 10%,l2=0.9l1.
Substitute l2=0.9l1 into the formula:
‌

r

R

=‌

l1−0.9l1

0.9l1

Simplify the numerator:
l1−0.9l1=0.1l1.
So,
‌

r

R

=‌

0.1l1

0.9l1

=‌

0.1

0.9

=‌

1

9

Therefore, r=‌

R

9