Module 6: Particles and Medical Physics Flashcards
(46 cards)
Define capacitance.
The amount of charge a capacitor can store per unit voltage.
Define the Farad.
Coulomb per volt.
Describe a Q against V graph
Gradient - Capacitance
Area under the graph - Energy stored
What is the time constant, τ, of a capacitor
- The time taken for V, I, or Q to decrease to ≅37% when discharging
- τ = RC, where R is the equivalent resistance of the circuit and C is the equivalent capacitance of the circuit.
C ∝ A/d, define these letters and explain the constant of proportionality.
C - Capacitance
A - Area of one plate
d- Distance between plates
The constant of proportionality is ε.
ε = εᵣε₀, where εᵣ is the relative permittivity of the material between the plates, and ε₀ is the permittivity of free space.
What are some uses of capacitors?
- Camera flash
- Touchscreen
- Back up energy supplies
- When AC is converted to DC, it smoothes the current, ideally τ > > T, where T is the period of the alternating current
Define an electrical field.
An electric field is a region where a charged particle experiences a force due to its charge.
Define electrical field strength.
The force per unit positive charge.
What do the direction of electrical fields lines show?
The direction of the force on a positive test charge.
What is a uniform electrical field?
A region where electrical field strength is constant, all the field lines are equally spaced and parallel.
A source of this type of field are parallel plate capacitors.
What is a radial electrical field?
A region where electrical field strength varies with distance according to an inverse square law.
A source of this type of field is a point charge or spherically symmetrical charge.
State Coulomb’s law.
The magnitude of the electrostatic force, F, between two point charges, Q and q, is directly proportional to the product of the charges, and inversely proportional to the square of the distance, r, between them.
Define electrical potential.
Electric potential at a point is the work done per unit positive charge to move the charge from infinity to that point
Define electrical potential energy.
Electrical potential energy at a point is the energy required to bring a positive charged particle from infinity to that specific point in the field.
What is a magnetic field?
A region where a moving charge or magnetic material experiences a force.
What do magnetic field lines show?
The direction of the force on a free north pole in that field.
What is magnetic flux density?
The magnetic flux, Φ, per unit area, A, perpendicular to the field lines.
What happens to a charged particle moving perpendicular to a magnetic field?
It undergoes circular motion with radius:
r = mv/Bq
What is Faraday’s Law of Electromagnetic Induction?
The induced emf is proportional to the rate of change of magnetic flux.
What is Lenz’s Law?
An induced current opposes the change in magnetic flux causing it.
What is the motor effect?
The motor effect describes the force experienced by a current-carrying conductor placed in a magnetic field, causing motion.
What are some applications of the motor effect?
Electric motors and loudspeakers
What is the generator effect?
The generator effect is the production of an emf, due to changing magnetic flux.
What does the size of an induced current when a conductor is moved relative to a magnetic field depend on?
The magnetic field strength, the length of the conductor in the field and the speed at which the conductor is moved.
