Electrostatic Potential and Capacitance quiz

The SI unit of electric potential is:

The work done in moving a charge along an equipotential surface is:

The electric field and potential are related by:

The capacitance of an isolated sphere of radius R is:

When a dielectric of constant K fills a capacitor, its capacitance becomes:

The equivalent capacitance of capacitors in series is:

The energy stored in a capacitor is:

Inside a charged conductor, the potential is:

One farad equals:

The potential at any point on the equatorial line of a dipole is:

Why is the electrostatic potential inside a charged hollow conductor constant? (2 marks)

Why do equipotential surfaces never intersect? (2 marks)

What is electrostatic shielding? (2 marks)

Write the expression for the potential energy of a dipole in a uniform electric field. (2 marks)

What is polarisation of a dielectric? (2 marks)

Why is the electric field perpendicular to an equipotential surface? (2 marks)

What happens to the capacitance if the separation between the plates is doubled? (2 marks)

Write the expression for energy density of an electric field. (2 marks)

Why does a bird sitting on a high voltage wire not get a shock? (2 marks)

Derive the expression for potential due to a point charge. (2 marks)

Charges of +2 microC and -2 microC are placed 6 cm apart. Find the potential at the midpoint and the potential energy of the system. (3 marks)

An air capacitor of 10 microF is filled with a dielectric of constant 5. Find its new capacitance. What happens to the charge if it remains connected to the same battery? (3 marks)

Capacitors of 2 microF and 3 microF are connected in series, and this combination is connected in parallel with a 4.8 microF capacitor. Find the equivalent capacitance. (3 marks)

Find the work done in moving a charge of 3 microC from a point at 40 V to a point at 100 V. (3 marks)

A parallel plate air capacitor has plates 2 mm apart and is charged to 6 V. Find the electric field between the plates and the energy density. (3 marks)

Read the passage and answer the questions. A defibrillator uses a 32 microF capacitor charged to 5,000 V. The stored energy is delivered to the heart of a patient in a few milliseconds to restore normal rhythm. (i) Find the energy stored. (ii) Find the charge stored. (iii) Why is a capacitor used instead of connecting the battery directly? (5 marks)

Read the passage and answer the questions. Smartphone touchscreens use a grid of tiny capacitors. When a finger touches the screen, the capacitance at that point changes and the phone detects the touch. (i) Why does a finger change the capacitance? (ii) Why does the screen not respond to a gloved finger? (iii) What is capacitance? (5 marks)

Read the passage and answer the questions. A student brings a charged rod near a hollow metal sphere resting on an insulating stand and finds that the electric field inside the sphere remains zero. (i) What is this phenomenon? (ii) Why is the field inside zero? (iii) Give one practical application. (5 marks)

Read the passage and answer the questions. The flash unit of a camera charges a 1,000 microF capacitor to 330 V and then discharges it through a flash tube in about a millisecond. (i) Find the energy stored. (ii) Find the average power during discharge. (iii) Why does the flash take a few seconds to recharge? (5 marks)

Read the passage and answer the questions. In a laboratory, a student inserts a mica sheet (K = 6) between the plates of a charged, isolated capacitor and notices that the voltmeter reading drops. (i) Why does the voltage drop? (ii) What happens to the charge? (iii) What happens to the stored energy? (5 marks)

Derive an expression for the electric potential due to an electric dipole at any point, and deduce the potential on the axial and equatorial lines. (6 marks)

Derive the capacitance of a parallel plate capacitor partly filled with a dielectric slab of thickness t and dielectric constant K. (6 marks)

Derive expressions for the equivalent capacitance of capacitors connected in series and in parallel, with diagrams. (6 marks)

Derive the expression for the energy stored in a capacitor and show that the energy density of an electric field is (1/2) epsilon0 E^2. (6 marks)

Explain equipotential surfaces with diagrams for a point charge, a dipole and a uniform field, and show that the field is the negative potential gradient. (6 marks)