Oscillations, Electric Fields & Capacitance Flashcards
Explain what is meant by the natural frequency of vibration of a system.
Frequency at which body will vibrate when there is no driving/external force acting on it.
Define forced frequency.
Frequency at which object is made to vibrate/oscillate.
State what is meant by simple harmonic motion.
Acceleration is directly proportional to displacement from equilibrium position, but acceleration is in opposite direction to displacement.
State, by refrence to simple harmonic motion, what is meant by angular frequency.
2π / Period
Identify the meaning of each symbol in the simply harmonic motion formulae:
a = -ω^(2)x
a = acceleration
ω = angular frequency
x = displacement from equilibrium position
State what is meant by damping.
Loss of total energy of a system due to resistive forces.
State what is meant by resonance.
Maximum amplitude of vibrations of an oscillating body when the forced frequency eqauls the natural frequency.
State what is indicated by the direction of an electric field line.
The direction of force on a postive charge.
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.
- Electrical field lines are radial
- Electric field lines appear to originate from centre of sphere
State coloumb’s law.
The Force between 2 point charges is proportional to the product of the charges and inversely proportional to the square of their seperation.
State what is meant by electric field strength.
The force per unit positive test charge.
What is the symbol ε₀ used in the equation for electric field strength defined as:
E=Q/4πε₀r^(2)
ε₀ : permittivity of free space
State similarities between electric field and gravitational field due to a point charge and point mass respectively.
- Both are radial
- Both decrease with distance
- Both have an inverse square variation
State similarities between gravitational potential due to a point mass and the electric potential due to a point charge.
- Inversely proportional to distance
- both are zero at infinite distance
State differences between electric field and gravitational field due to a point charge and point mass respectively.
- Gravitational field is always towards the mass.
- Electric field can be towards or away from the charge.
State differences between the gravitational potential due to a point mass and the electric potential due to a point charge.
Gravitational potential is always negative, while Electric potential can be positive or negative.
Define electric potential at a point.
It’s the work done per unit charge in moving a positive charge from infinity to the point.
State the relationship between electric potential and electric field strength at a point.
Field strength = - Potential gradient
Define the Coulomb.
A charge of 1C passes a point when a current of 1A flows for one second.
State what is meant by the capacitance of a parallel plate capacitor.
Ratio of charge stored in one plate of a capacitor to the potential difference across the capacitor.
Suggest why, when a capacitor is connected across the terminals of a battery, the capacitor stores energy, not charge.
Equal and opposite charges on the plates so no resultant charge, however, energy is stored as postitive and negative charges seperated.
State functions of capacitors in electric circuits.
- Smoothing
- Time delay
- Tuning
- Blocking d.c.
- Surge protection
- Temporary power supply
Define capacitance.
Ratio of charge stored across one plate of a capacitor to the potential difference across the capacitor.