Current electricity practice · Medium

When an unknowns resistance $6\,\Omega$ are connected in the left and right gaps of a meter bridge, the balance point is obtained at 50cm. If $3\,\Omega$ resistance is connected in parallel to resistance in right gap, the balance point is

One junction of a certain thermoelectric couple is at a fixed temperature ${T_r}$ and the other junction is at temperature $T$. The thermo-electromotive force for this is expressed by $E = k\left( {T - {T_r}} \right)\,\,\left[ {{T_0} - \frac{1}{2}\left( {T + {T_r}} \right)} \right]$. At temperature $T = \frac{1}{2}{T_0}$, the thermoelectric power is

Constantan wire is used in making standard resistances because its

To draw maximum current from a combination of cells, how should the cells be grouped?

The resistivity of a material is found to be $10^8 \Omega$ $-\mathrm{m}$. Then the material would be

Kirchhoff’s I and II laws are based on conversation of

A potentiometer having the potential gradient of $2\,\,mV/cm$ is used to measure the difference of potential across a resistance of $10\,\,ohm$. If a length of $50\,\,cm$ of the potentiometer wire is required to get the null point, the current passing through the $10\,\,ohm$ resistor is (in $mA$)

The electric current passes through a metallic wire produces heat because of

Assertion: Two electric bulbs of 50 and 100 W are given. When connected in series 50 W bulbs glows more but when connected parallel 100 W bulb glows more.

Reason: In series combination, power is directly proportional to the resistance of circuit . But in parallel combination, power is inversely proportional to the resistance of the circuit.

Assertion: Through the same current flows through the line wires and the filament of the bulb but heat produced in the filament is much higher than that in line wires.

Reason: The filament of bulbs is made of a meterial of high resistance and high melting point.

For two incandescent bulbs of rated power $P_1$ and $P_2$, if $P_1>P_2$, then

Forty electric bulbs are connected in series across a $220\,\,V$ supply. After one bulb is fused, the remaining $\mathrm{39}$ are connected again in series across the same supply. The illumination will be

The resistance of a conductor does not depend on

Water boils in an electric kettle in $15\,\,minutes$ after switching on. If the length of the heating wire is decreased to $\mathrm{2/3}$ of its initial value, then the same amount of water will boil with the same supply voltage in

The thermo emf $\mathrm{E}$ in volts of a certain thermocouple is found to vary with temperature difference $\theta$ in ${ }^{\circ} \mathrm{C}$ between the two junctions according to the relation $\mathrm{E}=30 \theta-\frac{\theta^2}{15}$, then the neutral temperature of thermocouple is

Which of the following acts as a circuit protecting device?

One junction of a certain thermo-couple is at a fixed temperature ${T_r}$ and the other junction is at temperature $T$. The thermo electric force for this is expressed by
$E = K\left( {T - {T_r}} \right)\,\,[\,{T_0}\,\, + \,\,\frac{1}{2}\left( {{T^2} + T_r^2)\,} \right]$
At temperature $T = {T_0}/2$ the thermoelectric power is

Electrical conductivity of insulators is

The charge flown through a resistance $\mathrm{R}$ in time $\mathrm{t}$ varies with time according to $\mathrm{Q}=\mathrm{at}-\mathrm{bt}^2$. The total heat produced in $\mathrm{R}$ by the time current becomes zero is :

If the temperature of cold junction of thermocouple is lowered, then the neutral temperature

In potentiometer a balance point is obtained, when:-

If a wire is stitched to four times its length then the specific resistance of the wire will:

Consider four conducting materials copper, tungsten, mercury and aluminium with resistivity ${\rho _C},{\rho _T},{\rho _M}$ and ${\rho _A},$ respectively. Then,

Incandescent bulbs are designed by keeping in mind that the resistance of their filament increases with the increase in temperature. If at room temperature, $\mathrm{100 }\,\mathrm{W,}\,\mathrm{ 60 }\,\mathrm{W}\,\mathrm{ and }\,\mathrm{40}\,\mathrm{ W}$ bulbs have filament resistances ${R_{100}},\,\,{R_{60}}\,\,\mathrm{and}\,\,{R_{40}}$, respectively, the relation between these resistances is

On passing the current in water voltmeter, hydrogen

The resultant resistance value of three resistors each of $r ~\Omega$ are connected in series is $x$. When given three resistances are connected in parallel, the resultant value is

Statement I : Specific resistance depends on nature of material and independent of temperature of the material.

Statement II : A wire of resistance $6 \Omega$ is drawn out so that its new length is four times its original length. The resistance of the new wire is $\mathbf{4 8 \Omega} \Omega$.

Statement III: Drift velocity is the average constant velocity acquired by free electrons inside a metal by the application of an electric field which results in current.

Which of the following is correct?

A $12\,\,HP$ motor has to be operated $8\,\,h/day$. How much will it cost at the rate of $50\,\,paise/kWh$h in $10\,\,days\,\,?$

The conductivity of a superconductor is

Mobility of free electrons in a conductor is :