chapter 22 - Electric fields

Question 1

What is an electric field?

Answer 1

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

Question 2

What is the definition of electric field strength?

Answer 2

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

Question 3

What are the units of electric field strength?

Answer 3

NC⁻¹ (or Vm⁻¹)

Question 4

What does ε0 represent?

Answer 4

permittivity of free space ( 8.85x10^-12)

Question 5

What does εr represent?

Answer 5

Relative permittivity (of a dielectric).

Question 6

What does the direction of an electric field line show?

Answer 6

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

Question 7

What does the spacing of electric field lines show?

Answer 7

Field strength.

Question 8

Are test charges positive or negative?

Answer 8

positive

Question 9

What units equivalent to Vm⁻¹

Answer 9

N C⁻¹

Question 10

When is the equation E = V/d used?

Answer 10

To find the uniform field strength between two parallel plates.

Question 11

What is a dipole?

Answer 11

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

Question 12

State Coulomb’s law in words.

Answer 12

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.

Question 13

What is electric potential difference?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

0

Question 16

What units are equivalent to a V?

Answer 16

J C⁻¹

Question 17

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

Answer 17

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

Question 18

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

Answer 18

electric Potential α 1/distance

Question 19

What is a uniform electric field?

Answer 19

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

Question 20

What is a radial field?

Answer 20

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

Question 21

What is a neutral point in an electric field?

Answer 21

A point at which the resultant field strength is zero

Question 22

Is electric field strength a vector or a scalar quantity?

Answer 22

Vector

Question 23

Is electrical potential a vector or scalar quantity?

Answer 23

Scalar

Question 24

State a similarity between electric and gravitational fields.

Answer 24

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.

Question 25

State two differences between electric and | gravitational fields?

Answer 25

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.

Question 26

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

Answer 26

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

Question 27

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

Answer 27

To calculate the capacitance on an isolated sphere.

Question 28

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

Answer 28

The radius of an isolated sphere.

Question 29

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

Answer 29

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

Question 30

explain a practical to detect electric fields?

Answer 30

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

Question 31

describe a practical to investigate coulombs law?

Answer 31

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