Electric Fields Flashcards
What if one of the charges becomes negative
Define electric field
An electric fields a region where a charge experiences a force
What charge does field lines show the direction for
For negative and positive charges what way do the field lines act towards the charged particle
Draw field lines for when a positive and negative charged particle meet
Also draw on equipotential
Draw field lines and equipotential for two identical point charges
Draw field lines for two uniform parallel plates
Between L & M, state which one has a greater magnitude of charge and explain your answer
L as it has more field lines coming out of it and it’s field lines are closer together
A student suggest that this is a gravitational field. Explain why it isn’t
Is not because in a gravitational field lines do not act away from the particle but here they act away from L
Define coulomb’s law of attraction
Force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of their seperation
Define an electric field strength and what direction does it act
Electric field strength is the force per unit charge that would experience a small positive test charge
Acts away from positive charge and towards negative charge
Draw graph for electric field strength against radius for a radial field
Define absolute electric potential energy
Give equation for absolute electric potential energy
Should you keep signs of charge when calculating potential energy
Work done in moving a charged object from infinity to that point in the electric field
Yes you should keep the sign as you can have either a positive or negative potential energy
What is a capacitor
And then give it’s definition
Process of capacitors when added to a circuit
In the equation C = Q/V, what always remains constant for a capacitor
Capacitance remains constant so charge is directly proportional to potential difference
How does a dielectric work
Define the time constant
Time contact is time in seconds it takes for charge to fall to 1/e of its original value
Equation for charging and discharging a capacitor
Use charge
Charging Q=Q0 (1-e^-t/RC)
Discharging Q=Q0e^-t/RC
Draw graphs for charging capacitor
As current is same for discharge you still use the equation I=I0e^-t/RC
Take natural logs for discharging equations, use charge as an example
B
True or false, Capacitance of a capacitor is amount of energy stored by capacitor when pd across plates is 1V
True
A
D
State how initial charge could be obtained from a graph of current against time
Determine area under the graph
Only do part ii)
Energy is lost through heating of wires or motor
Energy is lost in overcoming frictional forces in the motor
Capacitor will not drive motor when voltage becomes low
C) Explain why there is an increase in energy stored by capacitor when polythene sheet is pulled out between the played
C) in polar dielectric molecules align in field with positive charged end towards negative plate
Work is done on capacitor seperating the positively charged surface of dielectric from negatively charged plate
B
Capacitance increases for a disk making it brighter, explain why
Current is larger and more energy stored
c) calculate total horizontal deflection of particle that occurs when falling between the plates
Explain why time to fall vertically between the plates is independent of mass of a particle
Force on particle is F=mg, acceleration is equal to F/m, hence acceleration is always g
Time to fall dependent on distance and acceleration
State why two particles wity different masses and charges do not have same horizontal acceleration passing through an electric field
Mass is not constant, particle mass will vary
Charge on particle not constant
a = Eq/m
Electric field strength constant but charge and mass vary so they are unlikely to be the same
C
Potential is higher at X compared to Y
Moving from high to low potential
Electron is negatively charged so force it experiences us in opposite direction to the electric field
Electric field is directed from X to Y so it moves towards X
Since electron moves to a lower potential, it’s electric potential energy increases as it moves against force acting on it
A is correct answer
Last line says increases by 4.0 x 10^-16 J
Electric field always points from high potential to lower potential
Hence correct answer is B
Electrons travel in opposite direction to field lines
A is correct answer
D is correct answer
Not c because work done can also be negative so it cancels out
A
C
C
B
Define an electric potential at a point in an electric field
Work done of a positive charge in moving charge from infinity
Ome is radial field and the other is uniform
