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A Level Physics > Module 6: Chapter 22 - Electric Fields > Flashcards

Module 6: Chapter 22 - Electric Fields Flashcards

1
Q

What is an electric field?

A

The area around an object in which a charge would experience a force

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2
Q

What is the electric field strength?

A

The force per unit positive charge

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3
Q

What is the equation for the force acting upon an object within an electric field?

A

F = EQ
Force = Electric Field Strength x Charge

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4
Q

What are the rules for drawing electric field lines?

A
  • The arrow on an electric field shows the direction of the field
  • Electric field lines are always at right angles to the surface of a conductor
  • Closer electeric field lines represent greater electric field strength
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5
Q

What does a uniform electric field look like?

A

Equally spaced, parallel electric field lines

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6
Q

In what direction do electric field lines go?

A
  • Away from a positive charge
  • Towards a negative charge
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7
Q

Draw a diagram showing the electric field between 2 positive charges

A
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8
Q

Draw a diagram showing the electric field between 2 negative charges

A
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9
Q

Draw a diagram showing the electric field between a positive and a negative charge

A
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10
Q

Draw a diagram showing the electric field around a positive bar

A
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11
Q

Draw a diagram showing the electric field between a positive and a negative plate

A

Field in the centre is a uniform field

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12
Q

Draw a diagram showing the electric field between a positive sphere and a negative bar

A
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13
Q

A proton is accelerated from rest by a uniform electric field of field strength 2x10⁵ NC⁻¹. Mass of proton = 1.7x10⁻²⁷ kg. What is the time is takes to travel 5cm?

A

7.3x10⁻⁸s

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14
Q

What is coulombs law?

A

The force between 2 electric charges Q and q is proportional to Qq and inversely proportional to the square of their separation r

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15
Q

What are the 2 equations for the force between 2 charges?

(coulombs law)

A

F = kQq/r²

F = qQ/4πεₒr²

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16
Q

What is the value of the constant of proportiobality (k) in coulombs law?

A

k = 8.99x10⁹

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17
Q

What is the equation for the constant of proportionality (k) in coulombs law?

A

k = 1/4πεₒ

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18
Q

What is εₒ?

A

The permittivity of free space

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19
Q

What is the value of εₒ (permittivity of free space)?

A

8.85x10⁻¹²

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20
Q

What is the equation for electric field strength with varying distance?

A

E = Q/4πεₒr²

21
Q

What is the major difference between electric and gravitational fields?

A
  • Gravitational fields ALWAYS attract
  • Electric fields can both attract and repel
22
Q

What is the property that creates gravitational fields?

23
Q

What is the property that creates electric fields?

24
Q

What is the equation for the uniform electric field between 2 parallel charged plates?

25
Q

Explain why the electric field between 2 parallel plates is uniform:

A

A charge will experience the same force wherever it is placed between the plates

26
Q

What are the units for electric field strength?

A

NC⁻¹ or Vm⁻¹

27
Q

What is the equation for the capacitance on a parallel plate capacitor?

A

C = εA/d

d = separation between the plates

A = area of overlap of the plates

ε = εₒεᵣ
ε = permittivity of free space x relative permittivity

28
Q

How was it discovered that charge is quantized?

A

Millikan’s oil drop experiment

29
Q

Explain Millikan’s oil drop experiment

A

A mist of oil droplets are sprayed inside the chamber using an atomizer. The friction experienced by the oil droplets as they are sprayed caused some of them to become charged. The oil droplets then fell down due to gravity and some of them passed through the gap in the anode. A potential difference was then applied, causing the electric field to turn on. By carefully adjusting this potential difference they could cause an oil droplet to be suspended stationary in mid air. From this the charge on the oil droplet could be calculated:
Force from electric field = Weight
EQ = mg
Q = mg/E
Q = ρvg/E
The volume could be determined as the drops were modelled as perfect spheres (and the radius could be determined by measuring the terminal velocity of the drop as it fell without an electric field. Therefore the drag is equal to the weight and can be used to determine r)
This was repeated and it was found they were all multiples of the lowest charge found on any droplet, this was the elementary charge

30
Q

What is the equation for the work done on a charge within an uniform electric field?

A

W = Vq
Work done = Potential Difference x Charge

31
Q

Calculate the velocity an electron is accelerated to by a potential difference of 1.5V

A

730 kms⁻¹

32
Q

What is the mass of a proton?

A

1.673x10⁻²⁷kg

33
Q

How do you predict the motion of a charged particle travelling at a right angle to a uniform electric field?

A

Analyse the vertical and horizontal components of the motion independently

34
Q

How far will the electron “fall” from its path while in-between the 2 plates?

A

4.11x10⁻³m

35
Q

Explain Electric potential energy

A

If 2 attracting charges were put in an electric field, side by side, and then a force was applied on the negative charge in order to separate them, the work done to do this separation would be the electric potential energy difference (measured in joules) between the 2 charges in their new location

36
Q

How can you calculate the electric potential energy from a force-separation graph?

A

area under the curve

37
Q

What is the equation for electric potential energy (difference)?

A

E = Qq/4πεₒr

38
Q

Find the work done to move a charge from position 1 to position 2

39
Q

Calculate the electrical potential energy within a hydrogen atom if the electron is orbiting at a distance of 5.29x10⁻¹²m (in Electron Volts)

40
Q

What is electrical potential?

A

The work done to bring a unit positive charge from infinity to a point

41
Q

What is the equation for electrical potential?

A

V = Q/4πεₒr

42
Q

What is the electrical potential in the field of a 5nC point charge at a distance of 0.75m from the charge?

43
Q

What is the equation for the capacitance of a charged sphere?

A

C = 4πεₒr

44
Q

What is the equation for capacitance?

45
Q

What are equipotential lines?

A

Lines that link points of equal electric potential in an electric field

46
Q

What is the link between electric field lines and equipotential lines?

A

They are perpendicular to one another

47
Q

What are similarities between a graviational and an electric field?

A
  • Both produce a radial field
  • Field strength ∝ 1/r²
48
Q

What happens to the angle of deflection if the distance between the moving charge and stationary charge increases?

A

The angle of deflection decreases

A Level Physics (29 decks)

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