The electrostatic potential energy of a system consisting of two charges 7 µC and –2 µC (and with no external field) placed at (–9 cm, 0, 0) and (9 cm, 0, 0) respectively is:
1. 0.2 J
2. -0.7 J
3. -0.2 J
4. 0.7 J
How much work is required to separate two charges 7 µC and –2 µC (and with no external field) placed at (–9 cm, 0, 0) and (9 cm, 0, 0) infinitely away from each other?
1. 0.2 J
2. -0.7 J
3. -0.2 J
4. 0.7 J
The electrostatic potential energy of a system consisting of two charges 7 µC and –2 µC (in an external electric field E = A(1/r2); A = 9 × 105 C m–2) placed at (–9 cm, 0, 0) and (9 cm, 0, 0) respectively is:
1. 34 J
2. 49.3 J
3. 47 J
4. 43 J
A molecule of a substance has a permanent electric dipole moment of magnitude 10–29 C m. A mole of this substance is polarised (at low temperature) by applying a strong electrostatic field of magnitude 106 V m–1. The direction of the field is suddenly changed by an angle of . The heat released by the substance in aligning its dipoles along the new direction of the field is: (For simplicity, assume 100% polarisation of the sample).
1. 6 J
2. 8 J
3. 3 J
4. 4 J
Which one of the following is wrong?
1. | A comb run through one’s dry hair attracts small bits of paper. |
2. | Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting. |
3. | Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion. |
4. | A bird perches on a bare high power line and gets a fatal shock. A man standing on the ground touches the same line and nothing happens to the man. |
A slab of material of dielectric constant K has the same area as the plates of a parallel-plate capacitor of capacitance but has a thickness (3/4)d, where d is the separation of the plates. What is the capacitance of the capacitor when the slab is inserted between the plates?
A network of four 10 µF capacitors is connected to a 500 V supply, as shown in the figure. The equivalent capacitance of the network is:
A network of four 10 µF capacitors is connected to a 500 V supply, as shown in the figure. The charge on the capacitor is: (Note, the charge on a capacitor is the charge on the plate with higher potential, equal and opposite to the charge on the plate with lower potential).
A 900 pF capacitor is charged by a 100 V battery. The electrostatic energy is stored by the capacitor is U. If the capacitor is disconnected from the battery and connected to another 900 pF capacitor (as shown in the figure ) the electrostatic energy stored by the system is U'. The ratio of is:
Four charges are arranged at the corners of a square ABCD of side d, as shown in the figure. A charge is brought from to the centre E of the square, the four charges being held fixed at its corners. How much work is needed to do this?