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Physics > A2 - Electric Fields > Flashcards

A2 - Electric Fields Flashcards

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1
Q

Define electric field strength

A

The force per unit charge on a small positive test charge at a point in a field

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2
Q

What is the equation for electric field strength?

A

E=F/Q

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3
Q

What happens to field lines between a flat and a pointed plate?

A

The lines bend towards the point, this is the most concentrated point in the field.

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4
Q

Is electric field strength a vector or scalar measurement?

A

Vector

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5
Q

Is electric potential a vector or scalar measurement?

A

Scalar

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6
Q

What happens to the kinetic and potential energy as a positively charged object moves away from a negatively charged one?

A

Its potential increases, but its kinetic decreases.

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7
Q

What happens to the kinetic and potential energy as a positively charged object moves away from an other positively charged one?

A

The potential decreases, and kinetic increases.

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8
Q

Where is the charge on a VdG generator/

A

positive charge on the belt, caused by felt removing electrons, this is transferred to the dome by a metal contact. These charges repel each other.

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9
Q

What happens to the potential of the VdG generator as the +ve charge moves onto the dome? Why

A

The potential increases as the energy per unit charge to move a +ve test charge to that point is increasing as the field is becoming stronger since the dome is more positively charged.

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10
Q

What is an equipotential?

A

A line of constant potential energy for a test charge. This runs perpendicular to the field lines.

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11
Q

What is the potential gradient?

A

Negative of the change of potential for a positive test charge ?(per unit distance)?

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12
Q

How is field strength calculated from potential gradient?

A

It is the negative of it.

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13
Q

What is coulomb’s law?

A

The force between 2 charges = Qq/4(pi)E0 * 1/r^2

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14
Q

Unlike gravity, what can we have when we are considering potential?

A

Potential hills and wells as charges can attract or repel.

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15
Q

What is a point charge?

A

A small FUCKING POSITIVE test charge that has no effect on the field in which it is placed. Theoretically useful for calculating potential etc.

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16
Q

When considering a charge placed in a field, what can we assume about the charge?

A

It is always positive

17
Q

What is the ratio of distance vs total distance for two particles of charge C and 4C where the electric field strength is zero?

A

Use ratios to calculate:

1/3

18
Q

How do you calculate the force vectors and the resultant force at a point due to two charges?

A

Consider the charge to be positive. Draw proportionally sized arrows attracted to negative and repelled from positive.

Use tip to tail notation to show resultant force.

19
Q

What happens to the electric field lines between a plate and a pointed plate?

A

The field lines concentrate on the pointed plate.

20
Q

What is the potential gradient?

A

the change in potential for a test charge per meter. Curve for a radial field, straight line for a uniform field.

21
Q

What is the relationship between field strength and potential gradient?

A

Field strength is the negative of potential gradient.

22
Q

What happens when a VdG generator is switched on?

A

Positive charge builds up on the belt, as electrons are removed onto the pad. Electrons transferred from the dome leave an increasing positive charge on the dome.

23
Q

What is the expression for the work done moving a test charge Q from potential v1 to potential v2

A

w=Q(V2-V1)

24
Q

In a lightening conductor, where is the field strength greatest?

A

Where the curve is greatest i.e. at the top. The field strength is such that it can ionise air and cause the lightning to discharge through the conductor.

25
Q

What kind of motion do charged particles move in and why?

A

Parabolic motion as the force is always acting in one particular direction.

26
Q

What is the relationship between electric potential and distance?

A

1/r

27
Q

Is electric potential vector or scalar?

A

Scalar

28
Q

How do you find the total electric potential for a point charge between two positive charges?

A

Add the electric potential due to each

29
Q

What happens when an electron is moved from +ve plate to negative plate in terms of direction of force and change in electric potential?

A

Force towards +ve plate, EP increasing as Ek decreasing

30
Q

How do you calculate work done moving an object towards a planet?

A

Area under field strength-distance graph

31
Q

What is the shape of potential/distance graph?

A

-1/r

32
Q

What is the shape of field strength/distance graph?

A

1/r^2

33
Q

What direction to electric field lines point in?

A

Away from positive charge

Physics (9 decks)

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