Motional EMF

Q.

What is back emf

Q. A projectile is fired at an angle of ${45}^0$ with the horizontal. Elevation angle of the projectile at its highest point as seen from the point of projection is

1. 
2. 
3. 
4. 

Q.

What are tensor quantities?

Q.

A staircase contains three steps each 10 cm high and 20 cm wide figure. What should be the minimum horizontal velocity of a ball rilling off the uppermost plane so as to hit directly the lowest plane?

Q. A conducting wire frame is placed in a magnetic field which is directed into the paper. The magnetic field is increasing at a constant rate. The directions of induced current in wires AB and CD are

1. A to B and C to D
2. B to A and D to C
3. B to A and C to D
   
4. A to B and D to C

Q.

If the current I through a resistor is increased by 100% (assume that temperature remains unchanged), the increase in power dissipated will be

1. 100%

2. 200%

3. 300%

4. 400%

Q. A rod of length $l$ rotates with an uniform angular velocity $\omega$ about its perpendicular bisector. A uniform magnetic field $B$ exists parallel to the axis of rotation. The potential difference between the two ends of the rod is

1. Zero
2. $2B\omega l^2$
3. $\frac{1}{2}\omega B{l}^2$
4. $B\omega l^2$

Q. A uniform magnetic field is restricted within a region of radius $r$. The magnetic field changes with time at a rate $\frac{d\overrightarrow{B}}{dt}$. Loop $1$ of radius $R>r$ encloses the region $r$ and loop $2$ of radius $R$ is outside the region of magnetic field as shown in the figure below. Then the e.m.f. generated is

1. $-\frac{d\overrightarrow{B}}{dt}\pi r^2$ in loop $1$ and zero in loop $2$.
2. Zero in loop $1$ and zero in loop $2$
3. $-\frac{d\overrightarrow{B}}{dt}\pi r^2$ in loop $1$ and $-\frac{d\overrightarrow{B}}{dt}\pi r^2$ in loop $2$
4. $-\frac{d\overrightarrow{B}}{dt}\pi R^2$ in loop $1$ and zero in loop $2$

Q. A wire of length $l$ has a magnetic moment $M$. It is then bent into a semicircular arc. The new magnetic moment is

​​​​​​​$[$1 Mark$]$

1. $M$
2. $\frac{2M}{\pi }$
3. $\frac{M}{l}$
4. $M\times l$

Q. A proton, a deuteron and an $\alpha -$particle having the same kinetic energy enters a region of uniform magnetic field, moving at right angles to the magnetic field $B$. What is the ratio of the radii of their circular paths?

1. $1:\sqrt{2}:1$
2. $1:\sqrt{2}:\sqrt{2}$
3. $\sqrt{2}:1:1$
4. $\sqrt{2}:\sqrt{2}:1$

Q.

Define the unit of self-inductance.

Q.

How to identify AC or DC?

Q.

A coil of inductance $2H$ having negligible resistance is connected to a source of supply whose voltage is given by $V=3t$ volt (where $t$ is in second). If the voltage is applied when $t=0s$, then the energy stored in the coil after $4s$ is _______ $J$.

Q.

The geostationary orbit of the earth is at a distance of about 36000 km from the earth's surface. Find the weight of a 120-kg equipment placed in a geostationary satellite. The radius of the earth is 6400 km.

Q.

A solid metal cube of edge length $2cm$ is moving in the positive $y$ direction at a constant speed of $6m/s$. There is a uniform magnetic field of$0.1T$ in the positive $Z$ direction. The potential difference between the two faces of the cube perpendicular to the $X$ axis, is:

1. $1mV$

2. $6mV$

3. $12mV$

4. $2mV$

Q. A metallic square loop $ABCD$ is moving in its own plane with velocity $\overrightarrow{V}$ in a uniform magnetic field perpendicular to its plane as shown in fig. Then, an electric field induced

1. in $AD$, but not in $BC$
2. in $AB$ and $CD$ both.
3. neither in $AD$ nor in $BC$
4. in $AD$ and $BC$ both.

Q.

What is B in magnetic field?

Q.

A $100V$ AC source of frequency $500Hz$ is connected to an LCR circuit with $L=8.1mH$, $C=12.5\mu F$ and $R=10\Omega$, all connected in series. The potential difference across the resistance will be:

Q. Two identical simple pendulums A and B have the same point of suspension, having length $\ell$ each. They are displaced by an angle ($\alpha$ and $\beta$ are very small and $\beta >\alpha$) and released from rest. Find the time after which B reaches its initial position for the first time. Assume collision to be elastic and both pendulums move in the same plane.

1. $\pi \sqrt{\frac{\ell }{g}}$
2. $2\pi \sqrt{\frac{\ell }{g}}$
3. $\frac{\pi \beta }{\alpha }\sqrt{\frac{\ell }{g}}$
4. $\frac{2\pi \beta }{\alpha }\sqrt{\frac{\ell }{g}}$

Q. Two concentric circular loops of radii $0.08\text{m}$ and $0.1\text{m}$ carries current such that magnetic field at the centre is zero. If the current in the outer loop is $8\text{A}$ clockwise, then the current in the inner loop is

1. $6.4\text{A}$ anticlockwise
2. $6.4\text{A}$ clockwise
3. $8\text{A}$ anticlockwise
4. $3.2\text{A}$ clockwise

Q.

A straight wire of diameter 0.5 mm, carrying a current of 1A is replaced by another wire of 1mm diameter carrying the same current. The strength of magnetic field far away is

Q. If an alpha particle and a deuteron move with velocities of $v$ and $2v$ respectively, the ratio of their de-Broglie wavelengths will be

1. $1:\sqrt{2}$
2. $2:1$
3. $1:1$
4. $\sqrt{2}:1$

Q. A pair of parallel metal plates are kept with a seperation '$d$'. One plate is at a potential $+V$ and the other is at ground potential. A narrow beam of electrons enters the space between the plates with a velocity $v_0$ and in a direction parallel to the plates. What will be the angle of the beam with the plates after it travels an axial distance $L$?

1. $ta{n}^{-1}\left[\frac{eVL}{md{v}_0}\right]$
2. $ta{n}^{-1}\left[\frac{eVL}{md{v}_0^2}\right]$
3. $si{n}^{-1}\left[\frac{eVL}{md{v}_0}\right]$
4. $co{s}^{-1}\left[\frac{eVL}{md{v}_0^2}\right]$

Q. A conductor ABOCD moves along its bisector with a velocity of 1 m/s through a perpendicular magnetic field of 1 $wb/m^2$, as shown in fig. If all the four sides are of 1m length each, then the induced emf between points A and D is

1. 0
2. 1.41 volt
3. 0.71 volt ​
4. None of the above

Q. A rod $PQ$ is connected to the capacitor plates. The rod is placed in a magnetic field $\left(B\right)$ directed downward perpendicular to the plane of the paper. If the rod is pulled out of magnetic field with velocity $\overrightarrow{V}$ as shown in fig. Then, identify the correct statement :

1. Plate $M$ will be positively charged
2. Plate $N$ will be positively charged
3. both plates will be similarly charged
4. No charge will be collected on either plates

Q. An aircraft with a wing-span of 40 m flies with a speed of 1080 km $h^{-1}$ in the eastward direction at a constant altitude in the northern hemisphere, where the vertical component of earth's magnetic field is 1.75 ´ ${10}^{-5}$T. Then the emf that develops between the tips of the wings is

1. 2.1 V
2. 0.21 V
3. 0.5 V
4. 0.35 V

Q.

What is natural frequency of LC circuit?

Q. 11. If electric field in a region is given bywhere E, -5x103 N/C, I = 2 cm.then electric flux passing through the plane x =2 cm. The plane is a square of side 2 cm.

Q. A ring has radius 30cm and a charge of 2nc the electric potential on the axis of the ring at a distance of 40cm from the center will we

Q.

Can an electric field exist in a vacuum?