An uncharged aluminium block has a cavity within it. The block is placed in a region permeated by a uniform electric field which is directed upwards. Which of the following is a correct statement describing conditions in the interior of the block's cavity?

1. The electric field in the cavity is directed upwards

2. The electric field in the cavity is directed downwards

3. There is no electric field in the cavity

4. The electric field in the cavity is of varying magnitude and is zero at the exact center.

A capacitor is filled with an insulator and a certain potential difference is applied to its plates. The energy stored in the capacitor is U. Now the capacitor is disconnected from the source and the insulator is pulled out of the capacitor. The work performed against the forces of the electric field in pulling out the insulator is 4U. Then dielectric constant of the insulator is:

1. 4

2. 8

3. 5

4. 3

An insulator plate is passed between the plates of a capacitor. Then current(outside the capacitor):

1. Always flows from A to B

2. Always flows from B to A

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

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

For a uniform spherical positive distribution of charge over volume of radius R, the potential will be maximum:

1. on the surface

2. at the center

3. at a distance $\frac{R}{2}$ from the surface

4. at a distance $\frac{3R}{2}$ from the surface

A student charges a capacitor in such a manner that it stores energy of 1 J. Now he wants to increase the potential energy to 4 J. He should:

1. quadruple the potential difference across the capacitor without changing the charge

2. double the potential difference across the capacitor without changing the charge

3. double both the potential difference and charge

4. double the charge without changing the potential difference

An electron beam passes between two parallel plate electrodes as shown in the diagram. The bottom plate is kept at zero potential, while a slowly varying positive voltage is applied to the upper plate, as shown in the graph. After passing between the plates the beam hits a screen and makes spot. Ignoring gravity , the spot is:

1. deflected up

2. deflected down

3. deflected up then down

4. deflected down then up

A parallel plate capacitor is charged from a cell and then isolated from it. The separation between the plates is now increased.

1. the force of attraction between the plates will increased

2. the field in the region between the plates will not change

3. the energy stored in the capacitor will decrease

4. the potential difference between the plates will decrease

A parallel plate capacitor has a parallel sheet of copper inserted between and parallel to the two plates without touching the plates. The capacity of the capacitor after the introduction of the copper sheet is (Assume thickness of sheet is negligible) -

1. minimum when the copper sheet touches one of the plates.

2. maximum when the copper sheet touches one of the plates

3. does not vary for any positions of the sheet between the plates.

4. lesser than that before introducing the sheet.

A parallel plate capacitor is charged by connecting it to a battery. The battery is disconnected and the plates of the capacitor are pulled apart to make the separation between the plates twice. Again the capacitor is connected to the battery (with same polarity) then:

1. Charge from the battery flows into the battery after reconnection.

2. Charge from capacitor flows into the battery after reconnection.

3. The potential difference between the plates decreases when the plates are pulled apart.

4. After reconnection of battery, potential difference between the plates will immediately become half of the initial potential difference (just after disconnecting the battery)

A capacitor C is charged to a potential difference V and battery is disconnected. Now if the capacitor plates are brought close slowly by some distance:

1. some + ve work is done by external agent

2. energy of capacitor will decrease

3. energy of capacitor will increase

4. none of the above