EEM1

Question 1

Name the four fundamental forces in nature

Answer 1

Electromagnetic, gravitational, strong, weak

Question 2

What is electromagnetic?

Answer 2

it is a long range force, governing interactions over potentially considerable distances.

Question 3

What is the force carried by?

Answer 3

It is carried by the photon, and is responsible for the existence of electric and magnetic fields.

Question 4

What is Electrostatics?

Answer 4

Electrostatics is the study of charges at rest, or very nearly at rest

Question 5

What types of charges are there?

Answer 5

Positive and negative charges, like charges will repel, charges of opposite signs will attract.

Question 6

What do atoms consist of?

Answer 6

Combinations of electrons (negatively and positively charged), protons (positively charged) and neutrons (no charge). Electrons are considered fundamental particles. Protons and neutrons are made up of combinations of quarks.

Question 7

Where are the protons and neutrons located in an atom?

Answer 7

They cluster together in the nuclues of the atoms, a region area roughly 10^-15m across

Question 8

Where are the electrons in the atom?

Answer 8

They orbit the nucleus at a range of around 10^-10m and are held in place by the attractive force of the positively charged protons.

Question 9

What does it mean for an atom to be neutral?

Answer 9

The number of electrons and protons balance, so the net charge is zero. The number of protons is known as the atomic number of the element

Question 10

What happens if you remove or add one or more electrons to an atom?

Answer 10

If you remove one or more electrons from an atom you create a positive ion, if you add one or more you create a negative ion.

Question 11

What is ionization?

Answer 11

The process of gaining/losing an electron from an atom.

Question 12

What is meant by describing something as positively/negatively charge?

Answer 12

By negatively we mean there are more electrons than protons in that object and vice versa for positively charged objects.

Question 13

What is an conductor?

Answer 13

Conductors are materials which permit the easy movement of electric charge. Conductors have free electrons at the outer edges of each atom, which can move freely through the material.

Question 14

What is an insulator?

Answer 14

Insulators do not permit the flow of electric charge easily. They do not have the free electrons which conductors posses.

Question 15

What is induction?

Answer 15

The act or process by which an electric or magnetic effect is produced in an electrical conductor or magnetizable body when it is exposed to the influence or variation of a field of force

Question 16

Define Coulumb’s law qualitatively and quantitively

Answer 16

The magnitude of the electric force between two point charges is directly proportional to the product of the charges, and inversely proportional to the square of the distance between them.
F = k* (Iq1q2I/r^2)

Question 17

K =

Answer 17

9x10^9 Nm^2C^-2

Question 18

What is an Electric field?

Answer 18

The electric force on a charged body is exerted by the electric field created by OTHER charged bodies. A body A creates an electric field around it. The field exists whether or not there is another charge. If we put another charge in the field. Then that charge would experience the force exerted by the field

Question 19

Define electric field quantitively

Answer 19

E =F/q , if q positive the the force experience by the charge is in the same direction as the electric field, if negative then the force and field are in opposite directions.

Question 20

Electric field of a point charge

Answer 20

E=F/q= 1/4piellipson* IqI/r^2

Question 21

In electro statics the electric field at every point with the material of a conductor must be:

Answer 21

zero

Question 22

If we have a charge distribution made up of a series of point charges q1,q2,q3 etc, what is the total force and total electric field a charge q0 at point p would experience?

Answer 22

Total force: F0=F1+F2+F3+…. such that F1=qoE1, F2=q0E2 etc

Total electric field at P is then: E = F0/q0=E1+E2+E3+….

Question 23

What is an Electric field LINE?

Answer 23

It is an imaginary line, or curve, drawn through a region of space so that its tangent at any point is in the direction of the electric field vector at that point.

Question 24

What do electric field LINES show?

Answer 24

They show the direction of E(the electric field of the point charge in question), the spacing between the points indicates their magnitudes.

Question 25

The closer bunched together the lines are:

Answer 25

the stronger the field, and vice verse

Question 26

At any one point, the electric field has a unique direction-therefore, field lines can NEVER:

Answer 26

cross

Question 27

What does Work-energy theorem tell us?

Answer 27

That the change in KE during the displacement equals the total work done on the particle. Ka+Ua=Kb+Ub

Question 28

When a charge move from height ya to yb, the work done on the charge by the field is:

Answer 28

W (a to b) =q0E(ya-yb)

Question 29

If our test charge is negative, then U increase when it moves with the field, and:

Answer 29

decreases when it moves against the field.

Question 30

Electric potential energy U when the test charge q0 is at any distance r from q is

Answer 30

U= (1/4piellipson)*qq0/r

Question 31

If the two charges have the same sign, the the interaction is repulsive, so the work is:

Answer 31

positive and U positive

Question 32

If the charge have the opposite sign, then the interaction is attractive, so the work done is:

Answer 32

negative and U is negative.

Question 33

For every electric field due to a static charge distribution, the force exerted by that field is:

Answer 33

conservative.

Question 34

Now consider a charge q0 moving through a field that is caused by several ther point charges, not just one. What is the PE assoiciated with q0 at some point a??

Answer 34

U = (q0/4piellipson)*(q1/r1+q2/r2+q3/r3)

Question 35

To find the potential V due to a single charge q we use:

Answer 35

V= U/q0=1/4piellipson*q/r

Question 36

The magnitude of the charge on the electron can be used to define a unit of energy. When a particle with charge q moves from a point where the potential is Vb to a point where it is Va, the change in potential energy is:

Answer 36

Ua-Ub=q(Va-Vb) If q equals charge of electron and Va-Vb = 1V We have 1 eV = 1.602x10^-19J

Question 37

Inside conductors there is no:

Answer 37

Electric Field

Question 38

Outside of the conductor there is:

Answer 38

An electric field which behaves in the same way it would for a point charge with the same charge q.

Question 39

What is an equipotential?

Answer 39

An equipotential surface is a 3D surface on which the electric potential is the same at every point. If a test charge is moved from point to point on such a surface, the electric potential energy does not change.

Question 40

What can equipotential surfaces not do?

Answer 40

They cannot touch or intersect.

Question 41

Field lines and equipotential always meet at:

Answer 41

90 degrees to each other.

Question 42

Field lines are:

Answer 42

curves.

Question 43

Equipotential are:

Answer 43

curved surfaces.

Question 44

In regions where the electric field in stronger, equipotentials are:

Answer 44

closer together, and where the field is weaker, they are more spread out.

Question 45

Potential gradient:

Answer 45

gradV

Question 46

In what direction does the potential gradient point in?

Answer 46

The potential gradient points in the direction that V increases most rapidly with a change in position.

Question 47

What is the direction of E in relation to V?

Answer 47

E is the direction in which V decreases most rapidly, and is always perpendicular to the equipotential surface through that point.

Question 48

Potential gradient in vector notation:

Answer 48

E = -(i dV/dx+jdv/dy+kdV/dz)