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physics > chapter 22 - Electric fields > Flashcards

chapter 22 - Electric fields Flashcards

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1
Q

What is an electric field?

A

A region of space where a charge will experience an electrostatic force.

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2
Q

What is the definition of electric field strength?

A

The force per unit charge on a positive test charge placed at that point

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3
Q

What are the units of electric field strength?

A

NC⁻¹ (or Vm⁻¹)

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4
Q

What does ε0 represent?

A

permittivity of free space ( 8.85x10^-12)

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5
Q

What does εr represent?

A

Relative permittivity (of a dielectric).

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6
Q

What does the direction of an electric field line show?

A

The direction of the force exerted on a positive test charge.

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7
Q

What does the spacing of electric field lines show?

A

Field strength.

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8
Q

Are test charges positive or negative?

A

positive

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9
Q

What units equivalent to Vm⁻¹

A

N C⁻¹

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10
Q

When is the equation E = V/d used?

A

To find the uniform field strength between two parallel plates.

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11
Q

What is a dipole?

A

A pair of opposite sign charges separated by a small distance (e.g. a polar molecule like HCl)

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12
Q

State Coulomb’s law in words.

A

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

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13
Q

What is electric potential difference?

A

The work done per unit positive charge in moving between two points

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14
Q

What is the definition of absolute electric potential of a point?

A

The work done per unit positive charge to move from infinity to that point in the field.

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15
Q

What is the absolute electric potential an infinite distance from a 1C charge?

A

0

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16
Q

What units are equivalent to a V?

A

J C⁻¹

17
Q

What is the relationship between the electrostatic force between two point charges and their seperation distance?

A

It is inversely proportional to the square of separation OR inverse square law

18
Q

What is the relationship between the electric potential and distance from a point charge?

A

electric Potential α 1/distance

19
Q

What is a uniform electric field?

A

A region of space in which the electric field strength is the same at all points

20
Q

What is a radial field?

A

An electric field generated by a point charge OR a field that obeys the inverse square law.

21
Q

What is a neutral point in an electric field?

A

A point at which the resultant field strength is zero

22
Q

Is electric field strength a vector or a scalar quantity?

A

Vector

23
Q

Is electrical potential a vector or scalar quantity?

A

Scalar

24
Q

State a similarity between electric and gravitational fields.

A

Both obey inverse square law for field strength (around a point mass/charge). Both have infinite range. Both act between two objects at a distance.

25
Q

State two differences between electric and

gravitational fields?

A

Gravitational fields act on masses, electric fields on charges: electric fields are much stronger that gravitational fields: electric fields can be attractive or repulsive, gravitational fields are always attractive: potential is always negative in a gravitational field.

26
Q

When is the equation V = Q / (4 pi ε0 r) used?

A

To find the potential around a point charge/in a radial field.

27
Q

When is the equation C = 4 x pi x ε0 x R used?

A

To calculate the capacitance on an isolated sphere.

28
Q

What is represented by R in the equation C = 4 x pi x ε0 x R used?

A

The radius of an isolated sphere.

29
Q

What is the relationship between electric potential energy and electric potential?

A

EPE = V x q where q is the charge in the field.

30
Q

explain a practical to detect electric fields?

A

hang a uniformly charged sphere from a nylon thread, attach thin strip of gold foil to the bottom of a insulator, charge this gold foil by momentarily touching it on charged sphere, the charged foil will experience a electrostatic force when close to sphere and as they are both positive they will repel. the angle of the gold foil shows the electric field strength

31
Q

describe a practical to investigate coulombs law?

A

charge two metal balls attached to rods by momentarily touching them to a positive electrode. attach one two the top of a sensitive measuring balance (measuring scale) and then lower the other one down from above. record the distance (r) between balls and also reading on the balance. change r and measure results again. force should be inversely proportional to r^2

physics (18 decks)

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