Oscillations, Electric Fields & Capacitance

Question 1

Explain what is meant by the natural frequency of vibration of a system.

Answer 1

Frequency at which body will vibrate when there is no driving/external force acting on it.

Question 2

Define forced frequency.

Answer 2

Frequency at which object is made to vibrate/oscillate.

Question 3

State what is meant by simple harmonic motion.

Answer 3

Acceleration is directly proportional to displacement from equilibrium position, but acceleration is in opposite direction to displacement.

Question 4

State, by refrence to simple harmonic motion, what is meant by angular frequency.

Answer 4

2π / Period

Question 5

Identify the meaning of each symbol in the simply harmonic motion formulae:

a = -ω^(2)x

Answer 5

a = acceleration
ω = angular frequency
x = displacement from equilibrium position

Question 6

State what is meant by damping.

Answer 6

Loss of total energy of a system due to resistive forces.

Question 7

State what is meant by resonance.

Answer 7

Maximum amplitude of vibrations of an oscillating body when the forced frequency eqauls the natural frequency.

Question 8

State what is indicated by the direction of an electric field line.

Answer 8

The direction of force on a postive charge.

Question 9

For any point outside a spherical conductor, the charge on the sphere may be considered to act as a point charge at its centre.

By refrence to electrical field lines, explain this.

Answer 9

1. Electrical field lines are radial
2. Electric field lines appear to originate from centre of sphere

Question 10

State coloumb’s law.

Answer 10

The Force between 2 point charges is proportional to the product of the charges and inversely proportional to the square of their seperation.

Question 11

State what is meant by electric field strength.

Answer 11

The force per unit positive test charge.

Question 12

What is the symbol ε₀ used in the equation for electric field strength defined as:

E=Q/4πε₀r^(2)

Answer 12

ε₀ : permittivity of free space

Question 13

State similarities between electric field and gravitational field due to a point charge and point mass respectively.

Answer 13

1. Both are radial
2. Both decrease with distance
3. Both have an inverse square variation

Question 14

State similarities between gravitational potential due to a point mass and the electric potential due to a point charge.

Answer 14

1. Inversely proportional to distance
2. both are zero at infinite distance

Question 15

State differences between electric field and gravitational field due to a point charge and point mass respectively.

Answer 15

1. Gravitational field is always towards the mass.
2. Electric field can be towards or away from the charge.

Question 16

State differences between the gravitational potential due to a point mass and the electric potential due to a point charge.

Answer 16

Gravitational potential is always negative, while Electric potential can be positive or negative.

Question 17

Define electric potential at a point.

Answer 17

It’s the work done per unit charge in moving a positive charge from infinity to the point.

Question 18

State the relationship between electric potential and electric field strength at a point.

Answer 18

Field strength = - Potential gradient

Question 19

Define the Coulomb.

Answer 19

A charge of 1C passes a point when a current of 1A flows for one second.

Question 20

State what is meant by the capacitance of a parallel plate capacitor.

Answer 20

Ratio of charge stored in one plate of a capacitor to the potential difference across the capacitor.

Question 21

Suggest why, when a capacitor is connected across the terminals of a battery, the capacitor stores energy, not charge.

Answer 21

Equal and opposite charges on the plates so no resultant charge, however, energy is stored as postitive and negative charges seperated.

Question 22

State functions of capacitors in electric circuits.

Answer 22

1. Smoothing
2. Time delay
3. Tuning
4. Blocking d.c.
5. Surge protection
6. Temporary power supply

Question 23

Define capacitance.

Answer 23

Ratio of charge stored across one plate of a capacitor to the potential difference across the capacitor.