6.2: Electric Fields, F

Question 1

Define: Electric field

Answer 1

Region around a body in which other charged bodies feel a force due to the electric charge around the body

Question 2

Define: Electric field lines

Answer 2

Shape of the field and direction of the field lines at a point is the direction in which a small positive charge would move when placed at that point

Question 3

Define: Electric field strength

Answer 3

Force per unit positive charge (E=F/Q)

-Force that a charge of +1C would experience if it was placed in the electric field

Question 4

Describe the force between 2 opposite charges

Answer 4

If the charges are opposite then the force is attractive and the forces will be negative

Question 5

If they are like charges then the force is _________ and the force will be ________

Answer 5

If they are like charges then the force is repulsive and the force will be positive

Question 6

What relationship(/law) can be used to describe the distance of the charges and the force between them

Answer 6

• Inverse square law.

- The further apart the charges are, the weaker the forces between them

Question 7

What factor does the force F depend on? (in terms of electric field)

Answer 7

-Permittivity of the material between the two charges

ε0

Question 8

Define: Coulomb’s law

Answer 8

Electrical force F between two point charges is directly proportional to the product of their charges and is inversely proportional to the square of their separation
(F=Qq/4πε0r^2)

Question 9

How can a uniform electric field be produced

Answer 9

By connecting two parallel plates to the opposite poles of a battery

Question 10

Describe the field strength between two parallel plates

Answer 10

Field strength(E) is the same at all points between the two plates

Question 11

What does the Capacitance of a capacitor depend on?

Answer 11

-How easy it is to generate an electric field between 2 plates
-Depends on the dimensions of the capacitor
(C=ε0A/d)

Question 12

Describe the movement of charged particles through a uniform electric field

Answer 12

They move through uniforms fields like projectiles, where a particle of charge Q will experience a constant force (F=EQ)

Question 13

Describe the direction of travel (force acting upon) a charged particle will move in relation to field lines in a uniform electric field

Answer 13

• Positively charged = force is in the same direction as field lines (acceleration)
• Negatively charged = force is in the opposite direction to the field lines (acceleration)

Question 14

Describe the path a charged particle would take as it travels at an angle through a uniform electric field

Answer 14

Since the perpendicular components are independent = constant velocity in direction of field but an acceleration in the direction of field (Newton’s first law) ∴ creating a parabolic path

Question 15

Explain how an application of Newton’s second law in relation to uniform electric fields

Answer 15

Work done on a particle by the force (of the field) increases kinetic energy causing it to accelerate at a constant rate in the direction of the force (Newton’s 2nd law)

Question 16

Define: Permittivity

Answer 16

A constant (e) related to the size of the capacitance C of a capacitor.

Question 17

Define: Relative permittivity

Answer 17

A material which is the factor by which the capacitance of a capacitor (NOT COMPLETE)

Question 18

Define: Electric potential(V)

Answer 18

Work done per unit positive charge to move that charge from infinity to a point in the electric field
V=Q/4πε0r

Question 19

Define: Electric potential energy

Answer 19

Work done to move that charge from infinity to a point in an electric field
E=Qq/4πε0r

Question 20

Derive an expression for the capacitance of an isolated charged sphere(,assuming charge is evenly distributed)

Answer 20

• V=Q/C and V=Q/4πε0R, R= radius of sphere
• Q/C = Q/4πε0R ,cancel Q’s
• 1/C = 1/4πε0R
• C = 4πε0R

Question 21

What assumption is made when deriving the capacitance of an isolated charged sphere

Answer 21

As it is a charged sphere all the charge is concentrated in the centre ∴ we can treat it like a point charge

Question 22

List 3 differences between Gravitational fields and electric fields

Answer 22

• Gravitational fields are always attractive
• Objects can be shielded from an electric field
• Size of an electric field depends on the medium between the charges

Question 23

List 3 similarities between Gravitational fields and electric fields

Answer 23

• g is force per unit mass, E is force per unit positive charge
• Inverse square law
• V is zero at infinity