$A$ student connects a voltmeter,an ammeter,and a resistor as shown in the circuit. If the voltmeter reading is $20 \ V$ and the ammeter reading is $4 \ A$,then the resistance $R$ will be:

Consider the two following statements $A$ and $B$, and identify the correct choice given in the answers: $(A)$ Duddell's thermo galvanometer is suitable to measure direct current only. $(B)$ Thermopile can measure temperature differences of the order of $10^{-3} {}^{\circ}C$.

The deflection in a moving coil galvanometer falls from $25$ divisions to $5$ divisions when a shunt of $24\ \Omega$ is applied. The resistance of the galvanometer coil will be: (in $\Omega$)

$A$ galvanometer having internal resistance $10 \Omega$ requires $0.01 \ A$ for a full scale deflection. To convert this galvanometer to a voltmeter of full-scale deflection at $120 \ V$, we need to connect a resistance of

$A$ galvanometer of resistance $50\, \Omega$ is connected to a battery of $3\, V$ along with a resistance of $2950\, \Omega$ in series. $A$ full-scale deflection of $30$ divisions is obtained in the galvanometer. In order to reduce this deflection to $20$ divisions,the resistance in series should be.......$\Omega$

Two identical galvanometers are converted into a voltmeter and a millivoltmeter. As compared to the series resistance of the voltmeter,the series resistance of the millivoltmeter will be