Answer:
Ratio of length will be 
Explanation:
We have given time period of the pendulum when length is
is 
And when length is
time period 
We know that time period is given by

So
----eqn 1
And
-------eqn 2
Dividing eqn 2 by eqn 1

Squaring both side

Answer: Current, resistance and voltage are the quantities which are related by Ohm's law.
Explanation:
A law which states that electric current is directly proportional to voltage and inversely proportional to resistance is called Ohm's law.
Mathematically, it is represented as follows.

where,
I = current
V = voltage
R = resistance
This means that the quantities related by Ohm's law include current, voltage and resistance.
Thus, we can conclude that current, resistance and voltage are the quantities which are related by Ohm's law.
In a string of length L, the wavelength of the n-th harmonic of the standing wave produced in the string is given by:

The length of the string in this problem is L=3.5 m, therefore the wavelength of the 1st harmonic of the standing wave is:

The wavelength of the 2nd harmonic is:

The wavelength of the 4th harmonic is:

It is not possible to find any integer n such that
, therefore the correct options are A, B and D.