Lectures 8-14

Question 1

Thermal expansions

Answer 1

the tendency of a substance to change in size (length, area, volume) due to a change in its temperature

increasing temperature, increases the atoms energy which means they increase motion

Question 2

Thermal expansion equation

Answer 2

(delta)L = L0a(delta)T

(delta)L = change in length
L0 = original length
a = coefficient of linear expansion
(delta)T = change in temperature

Question 3

Charge

Answer 3

Charge depends on the distribution of the charge, and the nature of the material (whether it’s an insulator or conductor).

Question 4

mass and charge of electrons

Answer 4

charge of a single electron = -1.602x10^-19 C
mass of a single electron = 9.109x10^-31kg

number of electrons (n) = total mass of electrons/mass of single electron

totally charge = number of electrons x charge of one electron

Question 5

Colombo’s law

Answer 5

describes the force of attraction or repulsion between two charged particles. it states that the magnitude of the force between two charges is directly proportional to the product of their charges and the quantity being measured (force, intensity or field strength) is inversely proportional to the square of the distance between from the source.

Question 6

Coulomb’s law equation

Answer 6

F = k(q1)(q2)/r^2

F (proportional to) 1/r^2

F = magnitude of repulsive force (N)
K = coulomb’s constant
q1 and q2 = charges of 2 nuclei
r = distance between the centres if the two nuclei

Question 7

How to find charges from number of protons

Answer 7

number of protons x elementary charge

elementary charge = 1.602 x 10^-19 C

Question 8

Vectors

Answer 8

a quantity with both magnitude and direction

Question 9

Adding vectors (graph method) (order doesn’t matter)

Answer 9

1. draw the first vector with its tail at the origin or starting point
2. Place the tail of the second vector at the head (arrow end) of the first vector
3. repeat for any additional vectors
4. The resultant vector is drawn from the tail of the first vector to the head of the last vector

Question 10

Adding vectors (Component method)

Answer 10

1. decompose vectors into components
   If A has a magnitude of A and an angle of 0 its components are:
   Ax = Acos0 and Ay = Asin0
2. Sum the components along each axis
   Total x components: Rx = Ax + Bx
   Total y components: Ry = Ay + By
3. Determine the magnitude and Direction of the resultant vectors
   Magnitude: R = √R^2x + R^2y
   Direction: 0R = Tan^-1 (Ry/Rx)

Question 11

Resolving vectors in 2D

Answer 11

1. Separate into two components Horizontal component (x-axis, Ax) and vertical component (Y-axis, Ay)
2. Ax = ACos0, Ay = ASin0

Question 12

Electric field

Answer 12

A region around a charged object where other charges experience a force due to the electric charge. It’s a vector field that represents the influence a charge exerts on other charges in its vicinity.

Directed away from positive charges and towards negative charges.

Question 13

Key features of an electric field

Answer 13

1. source (created by an electric charge +q or -q)
2. Nature (a vector quantity)
3. Test charge (the electric field is defined based on the force experienced by a small positive test charge placed in the field)

Question 14

Electric field is defined at a point

Answer 14

as the force per unit positive charge placed at that point

E = F/q0

E = Electric field (N/C or v/m)
F = Force (N)
q0 = Test charge (C)

Question 15

Electric charge formula

Answer 15

E = k(Q)/r^2

E = Electric field magnitude
K = 8.99 x 10^9 N (Coulomb’s constant)
Q = charge creating the field
r = distance from the charge (m)

Question 16

Gauss’s law

Answer 16

Relates the electric flux through a closed surface to the charge enclosed within that surface.

Statement: electric flux is directly proportional to the net charge enclosed within that surface,

Equation: ∮E by dA = Q(Enclosed)/ϵ0

∮E by dA= The electric flux through a closed surface
Q(enclosed) = the total charge enclosed within the surface
ϵ0 = the permitting of free space (8.854 x 10^-12C^2)

Question 17

Electric flux

Answer 17

The measure of the quantity of electric field passing through a given surface.

symbol: ΦE

equation:
ΦE = E by A = EAcos0

E = electric field vector
A = area through which the electric field passes
0 = angle between the direction of the electric field and the normal to the surface

Question 18

Electrical potential

Answer 18

at a point in space is the amount of potential energy per unit charge that a small positive test charge would have at that point, it is a scalar quantity.

defined: the work done by an external force to move a positive test charge from infinity to that point, divided by the magnitude of the charge.

Equation: V = U/q

V = electric potential
U = electric potential energy
q = the magnitude of the test charge

Question 19

Electrical potential energy

Answer 19

the energy a charged object possesses due to its position in an electric field. the potential energy is relative to some reference point (usually taken as infinity where potential energy is 0)

defined: the energy stored in a charge due to its position in an electric field or the interaction between charges. the closer the charge to another opposite charge, the higher its electrical potential energy.

Equation: U = qV
U = electrical potential energy
q = charge
V = electrical potential at the point

Question 20

Potential differences

Answer 20

the difference in electric potential between two points in an electric field. represents the work needed to move a charge between these two points. a measure of the energy change per unit charge as the charge moves in the electric field.

mechanical potential difference: P = mgh or P = Fh
Electrial potential difference: U = qEs or U = Fs

Question 21

Capacitor

Answer 21

an electronic component that stores energy in an electric field. made up of two conductive plates separated by an insulating material called a dielectric.

When a voltage is applied across the plates, an electric field develops, and charge accumulates on the plates one late becomes positively charged and the other becomes negatively charged.

equation: C = Q/V
C = the capacitance (in farads)
Q = the charge stored on the plates
V = the potential difference across the plates

Question 22

Current

Answer 22

the flow of electric charge through a conductor, typically in the form of electrons moving through a wire.

defined: the rate at which charge flows through a conductor. measured in Amperes, 1 ampere is equal to 1 coulomb of charge passing through point in a circuit per second.

equation: I = Q/T
I = electric current
Q = charge
T = time (in seconds)

Question 23

Resistance

Answer 23

A measure of how much material or component resists the flow of electric current.

define: the opposition to the flow of electric current through a conductor or component in a circuit. depends on the properties of the material, the length and the cross-sectional area of the conductor, and the temperature.

equation: R =V/I
R = resistance
V = voltage across the component
I = current through the component