Questions From Board Papers
1. What is the ratio of electric field intensity at a point on the equatorial line to the field at a point on axial line when the points are at the same distance from the centre of the dipole?
2. For an isolated parallel plate capacitor of capacitance C and potential difference V, what will happen to (i) charge on the plates (ii) potential difference across the plates (iii) field between the plates (iv) energy stored in the capacitor, when the distance between the plates is increased? [Answer: (i) No change (ii) increases (iii) No change (iv) increases].
3. A storage capacitor on a RAM (Random Access Memory) chip has a capacity of 55pF. If the capacitor is charged to 5.3V, how may excess electrons are on its negative plate?[Answer: 1.8 ├Ч 10^9]
4. The potential at a point A is тАУ500V and that at another point B is +500V. What is the work done by external agent to take 2 units (S.I.) of negative charge from B to A.
5. In charging a capacitor of capacitance C by a source of emf V, energy supplied by the sources QV and the energy stored in the capacitor is ┬╜QV. Justify the difference.
Important Questions For Practice
1. A point charge Q is kept at the intersection of (i) face diagonals (ii) diagonals of a cube of side a. What is the electric flux linked with the cube in (i) & (ii)?
2. Using GaussтАЩs theorem in electrostatics, deduce an expression for electric field intensity due to a charged spherical shell at a point (i) inside (ii) on its surface (iii) outside it. Graphically show the variation of electric field intensity with distance from the centre of shell.
3. A conducting slab of thickness тАШtтАЩ is introduced between the plates of a parallel plate capacitor, separated by a distance d (t is less than d). Derive an expression for the capacitance of the capacitor. What will be its capacitance when t is equal to d?
4. A potential difference V is applied across a conductor of length L and diameter D. How are the electric field E and the resistance R of the conductor affected when (i) V is halved (ii) L is halved (iii) D is doubled.
Justify your answer.
5. What is an equipotential surface? Write three properties Sketch equipotential surfaces of (i) Isolated point charge (ii) Uniform electric field (iii) Dipole
Important Questions On 12th Physics Chapter 2
Charge is uniformly distributed over the conductor, q = 1.6 ├Ч 10^тИТ7 C
Electric field inside a spherical conductor is zero. This is because if there is field inside the conductor, then charges will move to neutralize it.
For the parallel combination of the capacitors, equivalent capacitor is given by Ceq the algebraic sum,
Therefore Ceq = C1 + C2 + C3 = 2 + 3 + 4 = 9 pF
Therefore, total capacitance of the combination is 9 pF.
If voltage supply remained connected, voltage between two plates will be constant.
Supply voltage, V = 100 V
Initial capacitance, C = 1.771 ├Ч 10тИТ11 F
New capacitance, C1 = kC = 6 ├Ч 1.771 ├Ч 10тИТ11 F = 106 pF
New charge, q1 = C1V = 106 ├Ч 100 pC = 1.06 ├Ч 10тАУ8 C
Potential across the plates remains 100 V.
The electric field intensity inside a cavity is zero, even if the shell is not spherical and has any irregular shape. Take a closed loop such that a part of it is inside the cavity along a field line while the rest is inside the conductor. Net work done by the field in carrying a test charge over a closed loop is zero because the field inside the conductor is zero. Hence, electric field is zero, whatever is the shape.
Hence, the tangential component of electrostatic field is continuous from one side of a charged surface to the other.
Hence, the tangential component of electrostatic field is continuous from one side of a charged surface to the other.
If a small test charge is released at rest at a point in an electrostatic field configuration, then it will travel along the field lines passing through the point, only if the field lines are straight. This is because the field lines give the direction of acceleration and not of velocity.
Electric field is discontinuous across the surface of a charged conductor. However, electric potential is continuous.