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A Level Physcis OCR A > 6.2 Electric Fields > Flashcards

6.2 Electric Fields Flashcards

1
Q

Define Electric Field

A

A region of space in which charged particles are subject to an electrostatic force.

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2
Q

What shape of field do point charges have?

A

Radial fields.

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3
Q

How can you model uniformly charged spheres?

A

As a point charge at the centre of the sphere.

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4
Q

What do field lines show?

A

The path a positive test charge would take when placed in an Electric Field.

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5
Q

Which direction do the field lines point?

A

Positive to negative – the lines always point away from a positive charge and towards a negative charge.

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6
Q

What effect does distance have on the strength of the electrostatic force?

A

The greater the distance, the weaker the force.

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7
Q

How is the strength of an Electric Field represented in a diagram?

A

By how close together the field lines are – the closer the lines, the stronger the field.

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8
Q

Define Electric Field Strength

A

Force per unit charge on a positive test charge placed in the field.

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9
Q

What is the formula for Electric Field Strength?

A 
E = F ÷ Q
E = Electric Field strength (NC-1)
F = Force (N)
Q = Charge (C)
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10
Q

What is Coulomb’s Law?

A

The force between any two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them.

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11
Q

What is the formula for the force between two point charges? (Coulomb’s Law)

A

F= Q1Q2/4pie permitivityoffreespace r2

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12
Q

Define permittivity

A

The ability of a material to transmit an Electric Field (how easily the atoms become
polarised).

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13
Q

What is the formula for the Electric Field Strength of a point charge?

A

E=Q/4pie permittivityoffreespace r2

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14
Q

Name some similarities between Gravitational and Electric Fields

A

● Both follow the inverse square law for the force.
● Point masses and point charges both produce a radial field.
● Newton’s law and Coulomb’s law formulae for force are very similar:
● Field strength is defined by force per unit charge/mass.

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15
Q

What is the formula for the work done when moving a charge in an Electric Field?

A

Work done = Force x Distance moved

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16
Q

Define potential at a point in an Electric Field

A

The work done per unit charge in moving a positive test charge from infinity to that point in the Electric Field.

17
Q

What is the formula for the potential at a point in an Electric Field?

A 
V = W ÷ Q
V = Potential (V)
W = Work done in moving the particle (J)
Q = Charge of the particle (C)
18
Q

What is the formula for the potential between two parallel plates?

A 
V = E x d
V = Potential (V)
E = Electric Field strength (NC-1)
d = distance between the plates (m)
19
Q

What is the formula for the capacitance of a parallel plate capacitor?

A 
C = AE0Er/d
C=capacitance
A=area of the plates
E0=permitivity of free space
Er=relative permeability of dielectric
d=distance between the plates
20
Q

What can the motion of charged particles in an Electric Field be modelled as?

A

Projectile motion: the two components of velocity are independent of each other.
Velocity perpendicular to the field is not affected, velocity parallel to the field is.

21
Q

How do you calculate the parallel component of velocity for a charged particle in a uniform Electric Field?

A
  1. First, calculate the time the particle is in the field (using time = distance/speed, where distance = length of charged plates and speed = velocity perpendicular to the field).
  2. Use a = F/m and F=Eq to calculate the acceleration of the particle while it is in the field (a = Eq / m).
  3. Substitute these values into V = u + at where u is the initial parallel velocity and V is the final parallel velocity.
22
Q

What is the formula for the potential near a point charge? (Coulomb’s Law)

A

V = Q/4pie E0 r

23
Q

What does the force-distance graph for a point/spherical charge look like?

A

Force is inversely proportional to the square of the distance.

24
Q

What does the area under a force-distance graph for a point/spherical charge represent?

A

The work done in moving the charge.

25
Q

What is the formula for electric potential energy near a point charge?

A 
E = V x q
E = electric potential energy (J)
V = potential (V)
q = charge of the point charge (C)
26
Q

What is the formula for the capacitance of an isolated sphere?

A

Isolated spheres can store charge, so technically they can be classed as capacitors. Using C = Q ÷ V and the formula for V (in terms of Coulomb’s law), you can derive the formula for capacitance:

27
Q

What is the formula for electric potential energy near a point charge? (Coulomb’s Law)

A

E = Q1Q2/4pie E0 r

A Level Physcis OCR A (21 decks)

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