Two Parallel Currents

Q. a galvanometer of resistance 50 ohm is connected to a battery of 3 V along with a resistance of 2950 ohm 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

Q. A wire carrying current $I$ has the shape as shown in the figure.


Linear parts of the wire are very long and parallel to $X$-axis while semi-circular portion of radius $R$ is lying in $Y-Z$ plane. Magnetic field at point $O$ is

1. $\overrightarrow{B}=-\frac{{\mu }_0}{4\pi }\frac{I}{R}\left(\pi \hat{i}+2\hat{k}\right)$
2. $\overrightarrow{B}=\frac{{\mu }_0}{4\pi }\frac{I}{R}\left(\pi \hat{i}-2\hat{k}\right)$
3. $\overrightarrow{B}=\frac{{\mu }_0}{4\pi }\frac{I}{R}\left(\pi \hat{i}+2\hat{k}\right)$
4. $\overrightarrow{B}=-\frac{{\mu }_0}{4\pi }\frac{I}{R}\left(\pi \hat{i}-2\hat{k}\right)$

Q. Two point charges in air, at a distance of $20\text{cm}$ from each other, interact with a certain force. At what distance from each other should these charges be placed in oil of relative permittivity $5$ to obtain the same magnitude of force of interaction?

1. $8.94\times {10}^{-2}\text{m}$
2. $7.94\times {10}^{-2}\text{m}$
3. $6.94\times {10}^{-2}\text{m}$
4. $5.94\times {10}^{-2}\text{m}$

Q. A galvanometer of resistance 100 ohm gives full deflection for a current of 10^-5 A. The value of shunt required to convert it into an ammeter of range 1 ampere is :- (1) 1 ohm (2) 10^-3 ohm (3) 10^-5 ohm (4) 100 ohm

Q.

Two identical metal balls with charges +2Q and -Q are separated by the same distance, and exert a force F on each other. They are joined by a conducting wire, which is then removed. The magnitude of the force between them will now be

Q. In the presence of an applied electric field $\left(\overrightarrow{E}\right)$ in a metallic conductor.

1. electrons move in the direction of $\overrightarrow{E}$.
2. electrons move in the direction opposite to $\overrightarrow{E}$.
3. electrons move in any direction randomly but slowly drift in the direction of $\overrightarrow{E}$.
4. electrons move randomly but slowly drift in a direction opposite to $\overrightarrow{E}$.

Q. A dipole of dipole moment p is placed in non-uniform electric field along x-axis. Electric field is increasing at the rate of 1 V per m then the force on dipole is

Q. a galvanometer of resistance, G is shunted by a resistance S ohm. to keep the main current in the circuit unchanged the resistance to be put in series with the galvanometer is

Q.

What would be the interaction force between two copper spheres each of mass 1 g, separated by distance 1 m, if the total electronic charge in them differed from the total charge of the nuclei by one percent.?

Q. Two long straight wires are set parallel to each other. Each carries a current i in the same direction and the separation between them is 2r. The intensity of the magnetic field midway between them is

1. 
2. 
3. 
4. Zero

Q. (a) Draw a labelled diagram of a moving coil galvanometer. Describe briefly its principle and working.

(b) Answer the following :

(i) Why is it necessary to introduce a cylindrical soft iron core inside the coil of a galvanometer.

(ii) Increasing the current sensitivity of a galvanometer may not necessarily increase its voltage sensitivity. Explain, giving reason.

Q.

If a charged particle does not experience any force in a magnetic field, then ________

Q. A power transmission line feeds input power at $2300\text{V}$ to a step-down transformer with its primary windings having $4000$ turns. The output power is delivered at $230\text{V}$ by the transformer. If the current in the primary coil of the transformer is $5\text{A}$ and its efficiency is $90\%.$ The output current would be

1. $45\text{A}$
2. $30\text{A}$
3. $15\text{A}$
4. $20\text{A}$

Q. a galvanometer , having resistance of 50 ohm gives a full scale deflection for a current of 0.05A the length of a resistance wire of area of cross section 2.97* 10^(-2)(cm^2) that can be used to convert the galvanometer into an ammeter which can read a max. of 5 A current is (specific resistance of the wire =5*10^(-7) ohm m)

Q. Sketch a graph which correctly represent variation of electric field E for a dipole at different points among the line connecting the two charges with procedure

Q. Two long parallel wires P and Q are both perpendicular to the plane of the paper with distance 5 m between them. If P and Q carry current of 2.5 amp and 5 amp respectively in the same direction, then the magnetic field at a point half way between the wires is

1. 
2. 
3. 
4. 

Q. A square frame of side $l$ carries a current $I$ and produces a magnetic field $B$ at its center, The same current is passed through a circular coil having same perimeter as that of square. The field at the center of the circular coil is $B_1$. Then the ratio $\frac{B_1}{B}$ is-

1. $\frac{{\pi }^2}{2}$
2. $\frac{{\pi }^2}{2\sqrt{2}}$
3. $\frac{{\pi }^2}{4\sqrt{2}}$
4. $\frac{{\pi }^2}{8\sqrt{2}}$

Q.

On what factor does the mutual inductance depend between two coils.

1. Cross-sectional area of the common core

2. The number of their turns

3. Permeability of the core

4. All of these

Q. A galvanometer has 36 ohm resistance. If a 4 ohm shunt is added to this, the fraction of current that passes through the galvanometer is- (1) 1/4 (2) 1/9 (3) 1/10 (4) 1/40

Q. An electric current is flowing in a very long pin as shown in the figure. The value of magnetic flux density at point $\text{O}$ will be-

1. $\frac{{\mu }_{0}i}{4\pi R}[\pi +2]$
2. $\frac{{\mu }_{0}i}{4\pi R}[\pi +1]$
3. $\frac{{\mu }_{0}i}{4\pi R}[\pi -2]$
4. $\frac{{\mu }_{0}i}{4\pi R}[\pi -1]$

Q. A square loop, carrying an eddy current $I$, is placed in a horizontal plane near a long straight conductor carrying a steady current $I_1$ at a distance $d$ from the conductor as shown in figure. The loop will experience

1. a net attractive force towards the conductor
2. a net repulsive force away from the conductor
3. a net torque acting upwards perpendicular to the horizontal plane
4. a net torque acting downwards normal to the horizontal plane

Q. A galvanometer of 100 ohm resistance yields complete deflection when 10 mA current flows. What should be the value of shunt so that it can measure currents upto 100 mA ? (1) 11.11 ohm (2) 9.9 ohm (3) 1.1 ohm (3) 4.4 ohm

Q. A moving coil galvanometer has following characteristics,
Number of turns = $80$, Area of coil =$50{\text{mm}}^2$, Resistance of coil = $20\Omega$, magnetic field = $0.2\text{T}$, torsional constant of the suspension wire = $5\times {10}^{-9}\text{N-m/rad}$.
Which of the following statements are correct.

1. The angular deflection produced due to a potential difference of $0.01\text{mV}$ is $0.08\text{div}$
2. Current sensitivity of the device is $160\text{div/mA}$
3. Voltage sensitivity of the device is $8\text{div/mV}$
4. All of the above.

Q. 92.An electric motor operate on 50V supply and current of 12A if the efficiency of motor is 30% what is resistance of winding of motor?

Q. 48. AB is 1 meter long …wire of 10ohm resistance .the other data are shown in the circuit diagram.Calculate, a)potential gradient along AB and b)length AO of the wire , when the galvanometer shows no deflection. Explain in detail each step

Q. An electron and a proton enters into a region of uniform magnetic field at right angles to the field with the same kinetic energy. They describe circular paths of radius $r_e$ and $r_p$ respectively. then-

1. $r_e=r_p$
2. $r_e<r_p$
3. $r_e>r_p$
4. $r_e$ may be less than or greater than $r_p$ depending on the direction of the magnetic field

Q.

The ratio of forces between two charges placed at a certain distance apart in air and at half the distance apart in medium of dielectric k is

A)1:4k

B)k:4

C)4k:1

D)4:k

Q. A charge $Q_1$ is placed at $O$ inside a hollow conducting sphere having inner and outer radii as $10\text{m}$ and $11\text{m}$ as shown in the figure. The force experienced by $Q_2$ at $P$ is $F_1$ when $Q_1$ is placed at the center and force experienced by $Q_2$ when $Q_1$ is placed at $O$ is $F_2$. Then $\frac{F_1}{F_2}$ is equal to

1. $1$
2. ${\left(\frac{12}{13}\right)}^2$
3. ${\left(\frac{13}{12}\right)}^2$
4. None of the above

Q. A long wire A carries a current of 10 amp. Another long wire B, which is parallel to A and separated by 0.1 m from A, carries a current of 5 amp in the opposite direction to that in A. What is the magnitude and nature of the force experienced per unit length of B
$[{\mu }_0=4\pi \times {10}^{-7}weber/amp-m]$

1. Repulsive force of $2\pi \times {10}^{-5}N/m$
   
2. Repulsive force of ${10}^{-4}N/m$
   
3. Attractive force of ${10}^{-4}N/m$
   
4. Attractive force of $2\pi \times {10}^{-5}N/m$

Q.

How do you increase the sensitivity of a meter bridge?