Physics

Q.

A charge q is placed at the center of the line joining two equal charges Q. The system of three charges will be in equilibrium if q is equal to

1. $\frac{-Q}{2}$
2. $\frac{-Q}{4}$
3. $\frac{+Q}{2}$
4. $\frac{+Q}{4}$

Q. Four charges equal to – Q are placed at the four corners of a square and a charge q is at its centre. If the system is in equilibrium the value of q is

1. $-\frac{Q}{4}(1+2\sqrt{2})$
2. $\frac{Q}{4}(1+2\sqrt{2})$
3. $\frac{Q}{2}(1+2\sqrt{2})$
4. $-\frac{Q}{2}(1+2\sqrt{2})$

Q.

An object is placed at a distance of 10 cm from a convex mirror of a focal length of 15 cm. Find the position and nature of the image.

Q.

The maximum height of projectile formula is ______.

Q. Four charges are arranged at the corners of a square ABCD, as shown in the figure. The force on the positive charge kept at the centre O is

1. zero
2. along the diagonal AC
3. perpendicular to side AB
4. along the diagonal BD

Q. An infinitely long straight conductor carries a current of $5\text{A}$ as shown. An electron is moving with a speed of ${10}^5\text{m/s}$ parallel to the conductor. The perpendicular distance between the electron and the conductor is $20\text{cm}$ at an instant. Calculate the magnitude of the force experienced by the electron at that instant.

1. $8\times {10}^{-20}\text{N}$
2. $4\times {10}^{-20}\text{N}$
3. $8\pi \times {10}^{-20}\text{N}$
4. $4\pi \times {10}^{-20}\text{N}$

Q.

The maximum electric field strength E due to a uniformly charged ring of radius r, happens at a distance x, where value of x is (x is measured from the centre of the ring)

1. x = R

2. $x=\frac{R}{2}$

3. $x=\frac{R}{\sqrt{2}}$

4. $x=\sqrt{2}R$

Q. A uniform rod of length $200\text{cm}$ and mass $500\text{g}$ is balanced on a wedge placed at $40\text{cm}$ mark. A mass of $2\text{Kg}$ is suspended from the rod at $20\text{cm}$ and another unknown mass ${}^{\prime }{m}^{\prime }$ is suspended from the rod at $160\text{cm}$ mark as shown in the figure. Find the value of $m$ such that the rod is in equilibrium.
$(g=10{\text{ms}}^{-2})$

1. $\frac{1}{2}\text{Kg}$
2. $\frac{1}{3}\text{Kg}$
3. $\frac{1}{6}\text{Kg}$
4. $\frac{1}{12}\text{Kg}$

Q.

What-is-p type-and-n type semiconductor?

Q. For a plane electromagnetic wave propagating in $x$-direction, which one of the following combination gives the correct possible directions for electric field $\left(E\right)$ and magnetic field $\left(B\right)$ respectively?

1. $-\hat{j}+\hat{k},-\hat{j}+\hat{k}$
2. $\hat{j}+\hat{k},\hat{j}+\hat{k}$
3. $-\hat{j}+\hat{k},-\hat{j}-\hat{k}$
4. $\hat{j}+\hat{k},-\hat{j}-\hat{k}$

Q. Three charges 4q, Q and q are in a straight line in the position of 0, $\frac{l}{2}$ and l respectively. The resultant force on q will be zero, if Q =

1. -q
2. -2q
3. $-\frac{q}{2}$
4. 4q

Q. Two identical charged spheres suspended from a common point by two massless strings of length $l$, are initially at a distance $d(d<<l)$ apart because of their mutual repulsion. The charges begins to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity $v$. Then $v$ varies as a function of the distance $x$ between the spheres as

1. $v\propto x^{\frac{1}{2}}$
2. $v\propto x$
3. $v\propto x^{-\frac{1}{2}}$
4. $v\propto x^{-1}$

Q.

A stone is thrown in a vertically upward direction with a velocity of $5m{s}^{-1}$. If the acceleration of the stone during its motion is $10m{s}^{-2}$ in the downward direction, what will be the height attained by the stone and how much time will it take to reach there?

Q. A particle is released from height $S$ from the surface of the Earth. At a certain height, its kinetic energy is three times of its potential energy. The height from the surface of earth and the speed of the particle at that instant are respectively

1. $\frac{S}{4},\sqrt{\frac{3gS}{2}}$
2. $\frac{S}{4},\sqrt{3gS}$
3. $\frac{S}{4},\frac{\sqrt{gS}}{2}$
4. $\frac{S}{2},\frac{\sqrt{3gS}}{2}$

Q.

What is the derivative of ${\sin }^2\left(x\right)$?

Q.

What are the differences between elastic and inelastic collisions?

Q. The half-life of a radioactive substance is $30$ minutes. The time (in minutes) taken between $40\%$ decay and $85\%$ decay of the same radioactive substance is

1. $60$
2. $15$
3. $30$
4. $45$

Q. Two small balls having equal positive charges $Q$ $\text{(coulomb)}$ on each are suspended by two insulating strings of equal length $L$ $\text{(metre)}$ from a hook fixed to a stand. The whole setup is taken in a satellite into space where there is no gravity $($state of weightlessness$)$. The angle between the two strings and the tension in each string is

1. ${180}^{\circ },\frac{1}{4\pi {ϵ}_0}\frac{Q^2}{4L^2}\text{N}$
2. ${75}^{\circ },\frac{1}{4\pi {ϵ}_0}\frac{Q^2}{L^2}\text{N}$
3. ${120}^{\circ },\frac{1}{4\pi {ϵ}_0}\frac{Q^2}{3L^2}\text{N}$
4. ${60}^{\circ },\frac{1}{4\pi {ϵ}_0}\frac{3Q^2}{2L}\text{N}$

Q.

An electric dipole is placed at an angle of 30° with an electric field intensity of 2 × ${10}^5$ N/C. It experiences a torque equal of 4 Nm. The charge on the dipole, if the dipole length is 2 cm, is

1. 5 mC
2. 8 mC
3. 7 μC
4. 2 mC

Q.

what is the charge in 75 Kg of electrons

Q. The escape velocity from the Earth's surface is $v.$ The escape velocity from the surface of another planet having a radius, four times that of Earth and same mass density is

1. $4v$
2. $v$
3. $2v$
4. $3v$

Q. A uniform conducting wire of length $12a$ and resistance $R$ is wound up as a current carrying coil in the shape of -

$\left(i\right)$ an equilateral triangle of side $a$.

$\left(ii\right)$ a square of side $a$.

The magnetic dipole moments of the coils in each case respectively are -

$I$ is the current through the coils.

Q. What is the amount of charge possessed by $1\text{kg}$ of electrons ?

1. $1.76\times {10}^{11}\text{C}$
2. $1.76\times {10}^{-9}\text{C}$
3. $1.76\times {10}^{-7}\text{C}$
4. $1.76\times {10}^{-5}\text{C}$

Q. 13. The force between two point charges in air is100 N. If the distance between them is increasedby 50%, then the force between two charges willbe nearly equal to(1) 50 N(3) 100 N(2) 56 N(4) 44 N

Q. Two point charges $Q_1$ and $Q_2$ exerts force $F$ on each other, when kept at certain distance apart. If the charge on each particle is halved and the distance between them is doubled, then the new force between the two particles would be

1. $\frac{F}{2}$
2. $\frac{F}{4}$
3. $\frac{F}{8}$
4. $\frac{F}{16}$

Q. Charges $Q_1$ and $Q_2$ are at points $A$ and $B$ of a right angle triangle $OAB$ see figure. The resultant electric feild at point $O$ is perpendicular to the hypotenuse, then $Q_1/Q_2$ is proportional to :

1. $\frac{x_1^3}{x_2^3}$
2. $\frac{x_2}{x_1}$
3. $\frac{x_1}{x_2}$
4. $\frac{x_2^2}{x_1^2}$

Q. Time interval measured by a clock given the following reading 1.25s, 1.24s 1.27s 1.21s, 1.28s what is% relative error

Q. An electric lift with a maximum load of $2000kg$ (lift + passengers) is moving up with a constant speed of $1.5{ms}^{-1}$. The frictional force opposing the motion is $3000N$. The minimum power delivered by the motor to the lift in watts is: $(g=10{ms}^{-2})$

1. $34500$
2. $23000$
3. $20000$
4. $23500$

Q. the main scale of a vernier calipers has n divisions/cm. n divisions of the vernier scale coincide with (n-1) divisions of the main scale. the least count of the vernier scale is

Q. In the circuits shown below, the readings of the voltmeter and the ammeter will be

1. $V_2>V_1$ and $i_1=i_2$
2. $V_2>V_1$ and $i_1>i_2$
3. $V_1=V_2$ and $i_1>i_2$
4. $V_1=V_2$ and $i_1=i_2$