Q. No.Two charges q1 and q2 are placed 30 cm apart, as shown in the figure. A third charge q3 is moved along the arc of a circle of radius 40 cm from C to D. The change in the potential energy of the system is , where k is:
1.
8q2
2.
8q1
3
6q2
4.
6q1
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If the dielectric constant and dielectric strength be denoted by k and x respectively, then a material suitable for use as a dielectric in a capacitor must have:
1. high k and high x.
2. high k and low x.
3. low k and low x.
4. low k and high x.
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Three capacitors of capacitances 3 μF, 9 μF and 18 μF are connected once in series and another time in parallel. The ratio of equivalent capacitance in the two cases will be:
1. 1 : 15
2. 15 : 1
3. 1 : 1
4. 1 : 3
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Four capacitors each of capacity 3 μF are connected as shown in the adjoining figure. The ratio of equivalent capacitance between A and B and between A and C will be:
1. 4: 3
2. 3: 4
3. 2: 3
4. 3: 2
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A parallel plate condenser is filled with two dielectrics as shown. Area of each plate is A metre2 and the separation is t metre. The dielectric constants are k1 and k2 respectively. Its capacitance in farad will be:
1.
2.
3.
4.
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In the connections shown in the adjoining figure, the equivalent capacity between A and B will be:
1. 10.8 μF
2. 69 μF
3. 15 μF
4. 10 μF
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The diagrams below show regions of equipotentials.
A positive charge is moved from A to B in each diagram. Then:
| 1. | the maximum work is required to move q in figure(iii). |
| 2. | in all four cases, the work done is the same. |
| 3. | the minimum work is required to move q in the figure(i). |
| 4. | the maximum work is required to move q in figure(ii). |
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A capacitor of 2 is charged as shown in the figure. When the switch S is turned to position 2, the percentage of its stored energy dissipated is:
| 1. | 20% | 2. | 75% |
| 3. | 80% | 4. | 0% |
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A parallel plate air capacitor of capacitance C is connected to a cell of emf V and then disconnected from it. A dielectric slab of dielectric constant K, which can just fill the air gap of the capacitor, is now inserted in it. Which of the following is incorrect?
| 1. | The potential difference between the plates decreases K times |
| 2. | The energy stored in the capacitor decreases K times |
| 3. | The change in energy stored is \({1 \over 2} CV^{2}(\frac{1}{K}-1)\) |
| 4. | The charge on the capacitor is not conserved |
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\(\mathrm{A}\), \(\mathrm{B}\) and \(\mathrm{C}\) are three points in a uniform electric field. The electric potential is:
| 1. | maximum at \(\mathrm{A}\) |
| 2. | maximum at \(\mathrm{B}\) |
| 3. | maximum at \(\mathrm{C}\) |
| 4. | same at all the three points \(\mathrm{A},\mathrm{B} ~\text{and}~\mathrm{C}\) |
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