Physics M.C.Q (1 Marks)

3. Parallel plate capacitor.

Explanation:
The simplest and the most widely used capacitor is the parallel plate capacitor. It consists of two large plane parallel conducting plates, separated by a small distance.

1. Zero.

Explanation:
We consider earth as the storage of infinite positive as well as a negative charge. Therefore, the potential of the earth is always considered to be zero and the potential of every body is measured with respect to earth. That’s why if we connect any charged body to the earth, its potential instantaneously becomes zero.

2. Polar molecules.

1. Permeability of the medium between the plates.

Explanation:
The capacitance of a parallel plate capacitor is directly proportional to the area of the plates and permittivity of the medium between the plates. It is indirectly proportional to the distance between the plates.

2. Van De Graaff generator.

2. Less than that of the first conductor.

2. Potential difference of the order of several million volts.

Explanation:
A Van de Graff generator, by means of a moving belt and suitable brushes, transfers charge continuously to a large spherical conducting shell. As a result, a potential difference of the order of several million volts is built up and this can be used for accelerating charged particles.

SELF

3. The field between the plates.

1. Decreases by a factor of 2.

1. W/Q *V.

1. Independent of the distance between the plates.

1. Mica

Explanation:
Here copper, tin, iron all are conductor so they will decrease the capacitance. The mica sheet is a dielectric or insulator so it will increase the capacitance k times. Where k is the dielectric constant.

3. Two capacitors in series and the third in parallel with the combinatioin of first two.

4. None of these

Explanation:
As the capacitor is charged by using cell so potential as well as filed between the plates become constant.
For removing dielectric the capacitance becomes C/ k. Thus capacitance decreases by a factor of k.

3. Equipotential surfaces are always spherical.

Explanation:
Equipotential surface
→ P.D difference between two points on the surface is zero always since potential is same everywhere in equipotential surface.
→ The EF is always perpendicular to the surface because there is no potential gradient along any direction parallel to the surface P so no EF parallel to the surface
→ Equipotential surface can have any shape not just sphere.
→ No work is done in moving a charge along the surface, because potential difference is zero.

4. Constant

Explanation:
Electric field at any point is equal to the negative of the potential gradient. But inside a conductor, the electric field is zero. Hence, the electric potential is constant throughout the volume of a conductor and has the same value on its surface.

1. A force and a torque.

1. Concentrically

Explanation:
We know that for a conducting sphere, the charge is always distributed on its outer surface. We also know that charge flows from higher potential to lower potential. But if we put the smaller sphere inside the larger sphere and connect them with a conductor, they will act as a single conductor and charge will be distributed to its outer surface, i.e. charge will flow to the larger sphere.

1. [I L T]

Explanation:
Dipole moment = charge × length of the dipole. The electric charge has dimensions [I T] and length has dimensions [L]. Therefore, the dipole moment has the dimension [I T L] and has unit C × m of C × m.

2. The reciprocal of the sum of the reciprocals of the individual capacitors.

Explanation:
The resultant capacitor when capacitors are joined in series is the reciprocal of the sum of the reciprocals of the indivisual capacitors.

3. Polar

Explanation:
A molecule in which the centre of mass of positive and negative charges does not collide with each other is called a polar molecule. They have a permanent dipole moment. They have unsymmetrical shapes.

4. Equipotential surface

Explanation:
Equipotential surface is a surface formed by the locus of all the points which are at the same potential. Equipotential surfaces do not intersect with each other and are closely spaced in the region of strong electric fields and vice-versa.

2. Positive to negative plate.

1. The facing surfaces of the capacitor have equal and opposite charges.
2. The two plates of the capacitor have equal and opposite charges.

4. The outer surfaces of the plates have equal charges.

Explanation:
In H.C Verma the answer is (a), (c), (d). But according to us the answer should be (a), (b), (d) all these options are the properties of a capacitor and the option (c) is incorrect because the battery is a source of energy not charge. Moreover if a capacitor plates have equal charge on outside and equal charge on inside then one can think that the charge on the plates must be also equal so option (b) cant be incorrect.

3. One charge is positive and other is negative.

1. increases

Explanation:
If the empty Condensor has capacity C, then its capacity with dielectric is given by C′ = kC, where k is the dielectric constant of the dielectric material. k can never be less than 1.

2. 50

Explanation:
The number of current pulses is equal to the frequency of the AC source because one current pulse passes through the diode for one oscillation of the AC source.

3. Electric potential.

Explanation:
Electric potential is equal to work done by an external agent in carrying a unit positive charge from the arbitrary chosen reference point to that point without any acceleration.

2. Flux is zero across the surface.

Explanation:
A dipole contains two equal and opposite charge. So total charge inside the sphere will be zero.
By Gauss's law, the flux across a surface is depends on the charge inside the surface. As total charge is zero inside the sphere so the flux through the sphere will be zero.
As the electric field is resultant effect due to all charges so there will be field exists on the surface.
As the sphere contains two equal and opposite charges so there may be exists equipotential surface in the sphere.

3. Both a and b.

2. Build up high voltage of few million volts.

1. Angular momentum about the hinge point of the ball will be max at lowest point.

Explanation:
Angular momentum about the hinge point of the ball will be max at point. mV will be max at closer point because law of conservation says that the swinging energy will be gathered when it will be at lowest point. The potential energy is maximum.

3. Decreases because the charge moves along the electric field.

The positive charge will experience an electrostatic force whose direction will be along the direction of electric field.
In other words, positive charge will move from high electrostatic potential to low electrostatic potential.
Work will be done by electric filed on the charge and the electric potential energy of the charge will decrease.

2. Increases K times.

2. V.

1. Zero

Explanation:
The electrostatic potential on the perpendicular bisector due to an electric dipole is zero.

3. Decreases, increases

Explanation:
When electron comes closer to the other stationary electron, its kinetic energy decreases because of repulsion between them. As per conservation of energy, the potential energy increases.

3. Electric potential at that point.

2. First flows from B to A and then from A to B

1. The plate voltage is zero.
2. The plate voltage is slightly negative.
3. The plate voltage is slightly positive.
4. The temperature of the filament is low.

Explanation:
The plate current varies directly with the plate voltage. Therefore, if the plate voltage is zero, the plate current is also zero. Due to the same reason, if the plate voltage is negative, the plate current will be zero. Now, if the plate is slightly positive, then it may be the reason that the plate voltage is not able to reduce the effect of space charge. Hence, the current may be zero. Now, as the temperature of the filament is low, it will not be able to emit electrons and the resulting plate current will be zero. Hence, all the options are possible.

3. Zero.

3. Zero.

Explanation:
Electric potential is a scalar quantity and its value is solely dependent on the charge near it and the distance from that charge. In this case, the point is equidistant from the two point charges and the point charges have the same value but opposite nature. Therefore equal but opposite potentials are generated due to the charges and hence the net potential at midpoint becomes zero.

1. Are closer in regions of large electric fields compared to regions of lower electric fields.
2. Will be more crowded near sharp edges of a conductor.
3. Will be more crowded near regions of large charge densities.

Equipotential surfaces are closer in regions of large electric fields because electric field intensity is inversely proportional to the separation between equipotential surfaces. 
As the electric field intensities is large near sharp edges of a charged conductor or near the regions of large charge densities. Therefore, numbers of equipotential surfaces are closer to such places or in other words they are more crowded.