An open organ pipe of length ' $l$ ' is sounded together with another open organ pipe of length $\left(l+l_1\right)$ in their fundamental modes. Speed of sound in air is ' $V$ '. The beat frequency heard will be ( $\left.l_1< < l\right)$

When a coil is connected to a d.c. source of e.m.f. 12 volt; then the current of 4 A flows in it . If the same coil is connected to a 12 volt, 50 Hz a.c. source, then the current flowing in it is 2.4 A . Then self-inductance of the coil will be

The ratio of work done by an ideal rigid diatomic gas to the heat supplied by the gas in an isobaric process is

A galvanometer has resistance $80 \Omega$ and it is shunted with resistance $20 \Omega$. If $20 \%$ of the main current flows through galvanometer, then what is the value of main current?