Electric Fields

Question 1

What is an electric field?

Answer 1

A region of space in which a charged particle experiences a force with its strength described as E

Question 2

Describe the relationship between Field strength, force and charge and state the equation.

Answer 2

Electric field strength at a point in space is equal to the force per unit charge on a small positive test charge placed in that position. E= F/Q

Question 3

What direction are the field lines of a positive point charge?

Answer 3

Out of/ away from the charge

Question 4

What direction are the field lines of a negative point charge?

Answer 4

Into/ towards the charge

Question 5

What unit is E, electric field strength, measure in?

Answer 5

N.C^-1 or V.m^-1
(Newtons per coulomb or Volts per metre)

Question 6

What is the relationship between distance and radial field strength?

Answer 6

As the distance from the source of the charge increases, the strength decreases (the lines are radial and so grow further apart)

Question 7

What is coulombs law?

Answer 7

The electrostatic force between two charges is directly proportional to the product of the charges; it is inversely proportional too the square of the distances between them.

Question 8

What is the equation for electrostatic force (coulombs law)

Answer 8

F = (k.Q1.Q2) / r²

Question 9

For radial fields ONLY, how do you calculate the electric field strength?

Answer 9

E = kQ / r²

Question 10

What is the electric potential?

Answer 10

The electric potential at a a point in a field is equal too the work done per unit charge in moving a small positive test charge from infinity too that point.

WORK DONE PER UNIT CHARGE

Question 11

What unit is electric potential measured in?

Answer 11

V (volts) or J/C

Question 12

What value is measured by taking the area under a field strength against distance graph?

Answer 12

Theoretical potential

Question 13

What is the equation for the electric potential?

Answer 13

Ve = k.Q / r

Question 14

What value can be taken as the area under a force against distance graph? (between two points)

Answer 14

Work done in moving a charge q from r1 to r2

Question 15

What is the equation for the work done in moving a charged particle?

Answer 15

ΔVe * q

(change in electric potential)

Question 16

What value can be taken as the gradient of a Electric potential (Ve) against distance graph?

Answer 16

E - electric field strength

Question 17

If a positive charge q is placed in a field, what direction is the force upon it in relation to the electric field?

Answer 17

The same direction as E, otherwise it is in the opposite direction.
(-ively charged)

Question 18

What is the electrical potential at infinity?

Answer 18

0V, by definition, Ve of a point in space is the work done moving a small positive test charge from infinity to that point.

Question 19

What equations apply too all fields? (F and W)

Answer 19

F = E/Q and ΔW = q.ΔV

Question 20

What is the numerical value of the constant k?

Answer 20

8.99 x 10^9 Nm²C-²

Question 21

What is the equation for the electrical potential energy? EPE

Answer 21

(k.Q.q) / r

Question 22

When a point charge is moved from a source, what energy transfer occurs?

Answer 22

The change in EPE is equal too the kinetic energy gained. (EPE decreases as the distance from the source increases)

Question 23

What is an equipotential?

Answer 23

A surface on which the electrical potential (Ve) is constant

Question 24

For a lone charge, how are equipotentials represented?

Answer 24

Spherical shells around the charge

Question 25

As the equipotentials grow further apart, what happens to E?

Answer 25

E decreases in strength

Question 26

What is the direction of the field strength relative too an equipotential?

Answer 26

Perpendicular, pointing in the direction of decreasing potential (towards the -ive charge)