Current Electricity · JEE Main previous year questions

A $10\Omega$, $20\text{ mH}$ coil carrying constant current is connected to a battery of $20\text{ V}$ through a switch. Now after switch is opened current becomes zero in $100\mu \mathrm{s}$. The average e.m.f. induced in the coil is ________ $\text{V}$.

1. A.$65\Omega$
2. B.$20\Omega$
3. C.$5\Omega$
4. D.$2\Omega$

A teacher in his physics laboratory allotted an experiment to determine the resistance (G) of a galvanometer. Students took the observations for $\frac{1}{3}$ deflection in the galvanometer. Which of the below is true for measuring value of G?

1. A.$\frac{1}{3}$ deflection method cannot be used for determining the resistance of the galvanometer.
2. B.$\frac{1}{3}$ deflection method can be used and in this case the G equals to twice the value of shunt resistances.
3. C.$\frac{1}{3}$ deflection method can be used and in this case, the G equals to three times the value of shunt resistances.
4. D.$\frac{1}{3}$ deflection method can be used and in this case the G value equals to the shunt resistances.

A resistor develops 300 J of thermal energy in 15 s, when a current of 2 A is passed through it. If the current increases to 3 A, the energy developed in 10 s is ____________ J.

Two cells of same emf but different internal resistances ${\mathrm{r}}_1$ and ${\mathrm{r}}_2$ are connected in series with a resistance R. The value of resistance R, for which the potential difference across second cell is zero, is :

1. A.$r_2-r_1$
2. B.$r_1-r_2$
3. C.$r_1$
4. D.$r_2$

1. A.AND gate
2. B.OR gate
3. C.NOR gate
4. D.NAND gate

If n represents the actual number of deflections in a converted galvanometer of resistance G and shunt resistance S. Then the total current I when its figure of merit is K will be:

1. A.$\frac{KS}{(S+G)}$
2. B.$\frac{(G+S)}{nKS}$
3. C.$\frac{nKS}{(G+S)}$
4. D.$\frac{nK(G+S)}{S}$

The length of a given cylindrical wire is increased to double of its original length. The percentage increase in the resistance of the wire will be ____________ %.

In a series LCR circuit, the inductance, capacitance and resistance are $\mathrm{L}=100\mathrm{mH}$, $\mathrm{C}=100\mu \mathrm{F}$ and $\mathrm{R}=10\Omega$ respectively. They are connected to an AC source of voltage $220\mathrm{V}$ and frequency of $50\mathrm{Hz}$. The approximate value of current in the circuit will be ____ $\mathrm{A}$.

What will be the most suitable combination of three resistors $\mathrm{A}=2\Omega$, $\mathrm{B}=4\Omega$, $\mathrm{C}=6\Omega$ so that $\left(\frac{22}{3}\right)\Omega$ is equivalent resistance of combination?

1. A.Parallel combination of A and C connected in series with B.
2. B.Parallel combination of A and B connected in series with C.
3. C.Series combination of A and C connected in parallel with B.
4. D.Series combination of B and C connected in parallel with A.

An object of mass $5\mathrm{kg}$ is thrown vertically upwards from the ground. The air resistance produces a constant retarding force of $10\mathrm{N}$ throughout the motion. The ratio of time of ascent to the time of descent will be equal to : [Use $\mathrm{g}=10\mathrm{m}{\mathrm{s}}^{-2}$].

1. A.$1:1$
2. B.$\sqrt{2}:\sqrt{3}$
3. C.$\sqrt{3}:\sqrt{2}$
4. D.$2:3$

A potentiometer wire of length $10\mathrm{m}$ and resistance $20\Omega$ is connected in series with a $25\mathrm{V}$ battery and an external resistance $30\Omega$. A cell of emf E in secondary circuit is balanced by $250\mathrm{cm}$ long potentiometer wire. The value of E (in volt) is $\frac{x}{10}$. The value of x is ____.

1. A.$1m/s$
2. B.$1cm/s$
3. C.$10^{2}m/s$
4. D.$10^{-2}cm/s$

Two resistors ${\mathrm{R}}_1=(4\pm 0.8)\Omega$ and ${\mathrm{R}}_2=(4\pm 0.4)\Omega$ are connected in parallel. The equivalent resistance of their parallel combination will be :

1. A.$(4\pm 0.4)\Omega$
2. B.$(2\pm 0.4)\Omega$
3. C.$(2\pm 0.3)\Omega$
4. D.$(4\pm 0.3)\Omega$

1. A.$3.75\mathrm{A}$
2. B.$2.35\mathrm{A}$
3. C.$2\mathrm{A}$
4. D.$2.73\mathrm{A}$

1. A.$6\mathrm{A}$
2. B.$25\mathrm{A}$
3. C.$10\mathrm{A}$
4. D.$0\mathrm{A}$

A uniform heating wire of resistance $36\Omega$ is connected across a potential difference of $240\mathrm{V}$. The wire is then cut into half and potential difference of $240\mathrm{V}$ is applied across each half separately. The ratio of power dissipation in first case to the total power dissipation in the second case would be 1 : x, where x is ____.

If you are provided a set of resistances $2\Omega$, $4\Omega$, $6\Omega$ and $8\Omega$. Connect these resistances so as to obtain an equivalent resistance of $\frac{46}{3}\Omega$.

1. A.$4\Omega$ and $6\Omega$ are in parallel with $2\Omega$ and $8\Omega$ in series
2. B.$6\Omega$ and $8\Omega$ are in parallel with $2\Omega$ and $4\Omega$ in series
3. C.$2\Omega$ and $6\Omega$ are in parallel with $4\Omega$ and $8\Omega$ in series
4. D.$2\Omega$ and $4\Omega$ are in parallel with $6\Omega$ and $8\Omega$ in series

An electric bulb of $500\text{ watt}$ at $100\text{ volt}$ is used in a circuit having a $200\text{ V}$ supply. Calculate the resistance R to be connected in series with the bulb so that the power delivered by the bulb is $500\text{ W}$.

1. A.$20\Omega$
2. B.$30\Omega$
3. C.$5\Omega$
4. D.$10\Omega$

The resistance of a conductor at $15^{\circ }\mathrm{C}$ is $16\Omega$ and at $100^{\circ }\mathrm{C}$ is $20\Omega$. What will be the temperature coefficient of resistance of the conductor?

1. A.$0.010^{\circ }{\mathrm{C}}^{-1}$
2. B.$0.033^{\circ }{\mathrm{C}}^{-1}$
3. C.$0.003^{\circ }{\mathrm{C}}^{-1}$
4. D.$0.042^{\circ }{\mathrm{C}}^{-1}$