Electric and Magnetic Fields Flashcards
What is a force field?
A region in which a non-contact force is experienced by a corresponding-interacting particle
What is an electric field?
A region in which a charged particle will experience a non-contact force
What is electric field strength?
The force per unit charge experienced by a charged particle when placed at a specific point in the field
State the equation used to find the force a charged particle experiences in an electric field?
F = EQ
Force = Electric Field Strength x Charge
Which law determines the magnitude of the electric force between two charges?
Coulomb’s Law
State Coulomb’s Law in words.
The force between two charges is directly proportional to the product of their charges and inversely proportional to the square of their separation
State Coulomb’s Law equation.
F = kQ₁Q₂ / r²
where k = 1/4πε₀
Describe the electric field pattern around a positive point charge.
A radial field, acting outwards
Describe the electric field pattern around a negative point charge.
A radial field, acting inwards
Describe the uniform electric field between two parallel plates.
Straight lines moving from the positive plate to the negative one, equally spaced
What equation is used to calculate the electric field strength between two parallel plates?
E = V /d
Electric Field Strength = Potential Difference / Separation
What is electric potential?
The amount of energy required to move a positive test charge from infinity to a given point in an electric field
How do you calculate the electric potential for a radial field?
V = kQ/r
where k = 1/4πε₀
What are equipotentials?
Lines in an electric field that have the same electric potential
How do you calculate the work done in moving a charge along an equipotential?
No work is done since the electric potential doesnt change, therefore no force is acting
What is ε₀?
Permittivity of free space ε₀ = 8.85 × 10−12 F m−1
What does a capacitor do?
It stores charge in a circuit
What two factors determine how much charge can be stored by a capacitor?
- Potential Difference across the capacitor
- Capacitance
What is capacitance?
A measure of how much charge can be stored by a capacitor per unit potential difference across it
State the equation used to calculate capacitance.
Q=CV —-> C = Q/V
Capacitance = Charge / P.d
What is the unit of capacitance?
Farads (F), CV⁻¹
What is represented by the area under a capacitor’s charge - potential difference graph?
The energy stored by the capacitor
What is the represented by the gradient of a capacitor’s charge - potential graph?
The capacitance of the capacitor
What are 3 equations to work out the energy stored by a capacitor?
W = 1/2 QV
W = 1/2 CV²
W = 1/2 Q²/C
Describe a charge-time graph for charging a capacitor, what does the gradient represent?
The charge increases rapidly to start with and then exponentially increases by a smaller amount. The gradient = Q/t = current
Describe a current-time graph for charging a capacitor, what does the area represent
It decreases dramatically do start with (looks like a y = 1/x graph)Area = It = charge
Describe a voltage-time graph for charging a capacitor?
Increases dramatically to start with and then drops off
What value is the product of the resistance and capacitance?
RC = τ (tau) the time constant
What does the time constant tell you?
The time it takes for the capacitor to reach 63% of its full charge and the time taken for it to discharge to 37% of its full-charge
