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Electric fields Flashcards

1
Q

What is coulombs law? (Look at equation book- first one in electric fields)

A

The force between 2 point charges in a vacuum is directly proportional to the product of their charges and inversely proportional to the square of the distance between the charges

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2
Q

What does a charged particle produce?

A

An electric field around it which exerts a force on another charged object

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3
Q

What are the units for electric field strength?

A

NC^-1 (newtons per coulomb)
and
Vm^-1 (volts per metre)

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4
Q

How is the direction of an electric field defined?

A

The direction of the force on a positive charge

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5
Q

Is electric field strength a vector or scalar?

A

Vector

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6
Q

How can a diagram show a uniform field?

A

When the field lines are equally spaced

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7
Q

How do field lines look like on a positive point charge?

A

equally spaced, radially, outwards

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8
Q

How do field lines look like on a negative point charge?

A

equally spaced, radially, inwards

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9
Q

How is potential gradient related to electric field strength?

A

potential gradient is equal to the magnitude of the field strength but is in the opposite direction

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10
Q

How can we find the potential difference between 2 points from a graph of electric field strength?

A

The area under the graph

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11
Q

What does the area under an electric field strength against r graph give?

A

The change of potential

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12
Q

What will happen to a moving charged particle when it enters a field?

A

It will change direction

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13
Q

What happens to charged particles in an electric field?

A

They experience a force

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14
Q

How can a charged particle move in the same direction in an electric field?

A

When it is parallel to the field

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15
Q

How does the field strength change as you move away from a point charge and how do we know?

A

It gets weaker because the field lines spread out

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16
Q

What is absolute electric potential

A

The potential energy per unit charge of a positive point charge at that point in the field

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17
Q

When is absolute electric potential energy at a maximum?

A

At the surface of a charge

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18
Q

Define electric potential

A

The work done per unit positive charge in moving it from infinity to that point

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19
Q

define potential difference

A

the work done against an electric field in moving unit charge from one point to a second point at a higher potential

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20
Q

What are lines of equipotential?

A

The lines connecting points of equal potential

21
Q

Are electric forces contact or non-contact forces?

A

non-contact forces

22
Q

What is the range of electric forces?

23
Q

What are capacitors?

A

Components of electrical circuits that temporarily store charge

24
Q

What is the structure of a capacitor?

A

2 parallel conducting plates separated by a thin insulating layer (dielectric) which are all encased in a metal or plastic

25
Define Capacitance
The ability of a capacitor to store charge per unit potential difference
26
What is the unit of capacitance?
The Farad
27
What is 1 Farad equal to?
1 CV^-1
28
What is the permittivity of a material?
The resistance of the material to an electric field passing through it
29
What are dielectric materials?
insulating materials where the molecules that make up the material can be polarised inside an electric field. Electric charges cant move through the field but the polar molecules align themselves within the field
30
What component in a circuit does not follow both decay and charging rules?
The current which only follows discharge
31
What is the time constant?
The time taken for the capacitor to drop to 37% of its initial value or the time taken to charge a capacitor to 63% of its initial value
32
How can you decrease the time in which the capacitor charges?
Keep resistance low
33
What assumptions are made in coulombs law?
Air is a vacuum The charge acts the centre of the sphere
34
How do the magnitudes of electrostatic forces and gravitational forces between subatomic particles compare?
The electrostatic force is significantly greater than the gravitational force because the masses are incredibly small whereas they have large charges
35
What is electric field strength?
The force per unit charge experienced by an object in an electric field
36
How do you calculate the work done by a moving charged particle between parallel plates?
Work done=QV
37
What will a charged particle travelling at right angles to the field experience? What shape will it follow?
A constant electric force Parabolic shape
38
When is electric potential energy zero?
At infinity
39
When is electric potential positive?
when charge is positive and the force is repulsive
40
When is electric potential negative?
when the charge is negative and the force is attractive
41
How do you find electric field strength from a graph of potential difference against radius?
Gradient of the tangent
42
Define electric potential difference?
The energy needed to move a unit charge between two points
43
What happens when a charge moves along an equipotential surface?
No work is done
44
How can you find the electric energy stored by a capacitor on a graph of charge against p.d?
The area underneath
45
How does a capacitor work?
When it is connected to a power supply a current starts to flow and a negative charge build up on the plate connected to the negative terminal. On the opposite plate electrons are repelled by the negative charge building up on the initial plate therefore electrons move to the positive terminal and an equal and opposite charge is forced on each plate creating a p.d.
46
What happens when the charge across the plates of a capacitor increases?
The p.d increases but the electron flow decreases due to the force of electrostatic repulsion also increasing
47
How do the current, charge and p.d across the capacitor decrease?
Exponentionally
48
Which value has the same equation for charging and discharging of a capacitor?
Current uses discharging each time
49
How do you find the time constant from a graph of lnQ against t?
-1/ gradient

Physics (10 decks)

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