Charging by Friction

Q. Force between two identical spheres charged with same charge is $F$. If $50\%$ charge of one sphere is transfered to the other sphere keeping the distance between them same, then the new force between spheres will be

1. $\frac{3}{4}F$
2. $\frac{3}{8}F$
3. $\frac{3}{2}F$
4. None of these

Q. Two concentric conducting sphere of radii R and 2R are carrying charges Q and -2Q respectively. If the charge on inner sphere is doubled, the potential difference between the two spheres will (1)becomes two times (2)becomes four times (3)be halved (4)reamins the same

Q.

What is a transistor and its symbol?

Q. When a glass rod is rubbed with silk, it

1. Gains protons from silk
2. Gains electrons from silk
3. Gives electrons to silk
4. Gives protons to silk

Q. Two short electric dipoles are placed as shown in figure.


The energy of electric interaction between these dipoles will be :

$[\text{Take}k=\frac{1}{4\pi {\epsilon }_0}]$

1. $$\frac{2k{p}_1{p}_2\cos \theta }{r^3}$$
2. $$\frac{-2k{p}_1{p}_2\cos \theta }{r^3}$$
3. $$\frac{-2k{p}_1{p}_2\sin \theta }{r^3}$$
4. $$\frac{-4k{p}_1{p}_2\cos \theta }{r^3}$$

Q. A sphere encloses an electric dipole within it. The total electric flux through the sphere is?

1. Zero
2. Double of that due to a single charge
3. Half of that due to a single charge
4. Dependent on the position of dipole inside sphere

Q.

If an object made of substance A is rubbed with an object made of substance B, then A becomes positively charged and B becomes negatively charged. If, however, an object made of substance A is rubbed against an object made of substance C, then A become negatively charged. What will happen if an object made of substance B is rubbed against an object made of substance C?

1. B becomes positively charged and C becomes positively charged.

2. B becomes positively charged and C becomes negatively charged.

3. B becomes negatively charged and C becomes positively charged.

4. B becomes negatively charged and C becomes negatively charged.

Q. When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs ofbodies. Explain how this observation is consistent with the law ofconservation of charge.

Q. 5. if identical charges (-q) are placed at each corner of a cube of side B, then electric potential of charge (+q) which is placed at centre of the cube will be A. 82q/4^° b B. 82q/^° b C. -42q/^° b D. -4q/3^° b

Q. A charge Q is distributed over two concentric hollow spheres of radii r and R (>r) such that the surface densities are equal. The potential at the centre is

Q.

Two conducting spheres of radii r1 and r2 are equally charged.The ratio of their potential is?

Q.

What is the active region for transistors?

1. The active region is that region in which the emitter-base junction is forward bias while the collector-base junction is also forward bias.

2. The active region is that region in which the emitter-base junction is forward bias while the collector-base junction is reverse bias.

3. The active region is that region in which the emitter-base junction is reverse bias while the collector-base junction is reverse bias.

4. The active region is that region in which the emitter-base junction is reverse bias while the collector-base junction is forward bias.

Q. If the magnitude of intensity of electric field at a distance $x$ on axial line and at a distance $y$ on equatorial line for a given dipole are equal, then $x:y$ is

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

Q.

What are the different applications of electrostatics?

Q. Why is the Base very thin in a transistor?

Q.

Choose the correct statement

1. The total positive charge of the universe is constant

2. The total negative charge of the universe is constant

3. The total charge of the universe is constant

4. The total charge particles in the universe remains constant

Q. Find the flux of the electric field through surface $\text{ABCD}$ of the inclined plane as shown in figure.

1. $Eab\cos \theta$
2. $Eab\sin \theta$
3. $Eab\tan \theta$
4. $Eab\cot \theta$

Q. two particles A and B having charges q and 2q respectively are placed on a smooth table with a seperation d.A third partcle C is to be clamped on the table in such a way that particles A and B remain at rest under electrical forces.What should be charge on C and where should it be clamped?

Q.

Point charge Q is placed at distance r from the centre of conducting sphere of radius R (r>R) which of the following is correct

1. The potential at centre is zero

2. The potential at centre is kq/r

3. The charge Sphere is zero

4. Both 2 and 3

Q. Charges $Q_1$ and $Q_2$ lie inside and outside respectively of a closed surface $\text{S}$. Let $E$ be the field at any point on $\text{S}$ and $\varphi$ be the flux of $E$ over $\text{S}$. Choose the correct statement (s).

1. If $Q_1$ changes in magnitude , both $E$ and $\varphi$ will change
2. If $Q_2$ changes in magnitude, $E$ will change but $\varphi$ will not change
3. If $Q_1=0$ and $Q_2\ne 0$, then $E\ne 0$ but $\varphi =0$
4. If $Q_1\ne 0$ and $Q_2=0$, then $E=0$ but $\varphi \ne 0$

Q. A capacitor of capacitance $C$ has charge $Q$ and resultant energy stored in it is $W$. If the charge on its plates is increased to $2Q$, the stored energy would be

1. $\frac{W}{2}$
2. $2W$
3. $\frac{W}{4}$
4. $4W$

Q. A non-conducting infinite rod is placed along the z-axis, the upper half of the rod (lying along $z\ge 0$ ) is charged positively with a uniform linear charge density $(z<0)$ is charged negatively with a uniform linear charge density $-\lambda$. The origin is located at the junction of the positive and negative halves of the rod. A uniformly charged annular disc (surface charge density: ${\sigma }_0$ ) of outer radius $2R$ is placed in the $x-y$ plane with its centre at the origin. The force on the rod due to the disc is $\frac{y{\sigma }_0\lambda R}{8{\epsilon }_0}$. Find the value of $y$.
Diagram

Q. Three charges are kept on a straight line as shown in figure. With $A$ and $B$ denoting arbitrary constants, the potential at a far-off point $(r>>a)$ on the axis is given by

1. $\frac{A}{r}$
2. $\frac{A}{r^2}$
3. $\frac{A}{r^3}$
4. $\frac{A}{r^2}+\frac{B}{r^3}+.....$

Q. The strain–stress curves of three wires of different materials are shown in the figure. $P$, $Q$ and $R$ are the elastic limits of the wires. The figure shows that

1. Elasticity of wire $P$ is maximum
2. Tensile strength of $R$ is maximum
3. Elasticity of wire $Q$ is maximum
4. None of the above is true

Q.

Two copper surfaces of same radii, one hollow and other solid are charged to same potential.Which of these will have more charge?

Q. 128.Find the electrostatic force of interaction between the two halves of a spherical conductor of radius R carrying a charge Q

Q.

Write the precautions that should be taken while using electricity?

Q. Identify the semiconductor devices whose characteristics are given below, in the order (a), (b), (c), (d)

1. Simple diode, Zener diode, Solar cell, Light dependent resistance
2. Zener diode, Simple diode, Light dependent resistance, Solar cell
3. Solar cell, Light dependent resistance, Zener diode, Simple diode
4. Zener diode, Solar cell, Simple diode, Light dependent resistance

Q. Explain clearly the function and working of p-n-p transistor and n-p-n transistor .

Q. Three charges 2q, Q, q are placed in a straight line of length l at points distance, 0, $\frac{1}{2}$ and l respectively. What should be ‘Q’ in order to make the net force on ‘q’ is zero.

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