Topic 1: Basic Concepts and Ohm's Law

Question 1

What is the charge of an electron?

Answer 1

-1.6 x 10^(-19) C (Coulombs)

[-1e charge]

Question 2

What is the charge of a proton?

Answer 2

1.6 x 10^(-19) C (Coulombs)

[+1e charge]

Question 3

What is the definition of an electrical current?

Answer 3

Rate at which charge is flowing.

Question 4

What is the definition of voltage?

Answer 4

Difference in charge between 2 points.

Question 5

What is the definition of resistance?

Answer 5

A component’s tendency to resist the flow of charge.

Question 6

What is electricity?

Answer 6

Electricity is the movement of electric charge.

Question 7

What is the formula to calculate the magnitude of current?

Answer 7

i(t) = [dq(t)/dt]

Question 8

What is the unit of current?

Answer 8

i(t) = A = C(s^(-1))
Amperes = Coulombs per second

Question 9

What is the formula to calculate charge?

Answer 9

q(t) = {integral from t1 to t2} i(t) dt

The integral of i(t) from t1 to t2 in terms of t.

Question 10

What is the unit of charge?

Answer 10

q(t) = C

Coulombs

Question 11

How does current flow?

Answer 11

Current always flows from high potential/voltage to low potential/voltage.

Question 12

What is the formula used to calculate resistance?

Answer 12

R = ρ x (L/A)

R= resistance (Ohms - Ω)
ρ = resistivity (Ohm.metres - Ω.m)
L = length of wire (metres - m)
A = cross-sectional area (metres squared - m²)

Question 13

What is the definition of conductance?

Answer 13

Conductance (G) is the reciprocal of resistance (R).

Question 14

What is the unit of conductance?

Answer 14

Siemens (S)

Question 15

What is the definition of conductivity?

Answer 15

Conductivity (σ) is the reciprocal of resistivity (ρ).

Question 16

What is the unit of conductivity?

Answer 16

Siemens per metre (S/m or S(m^-1))

Question 17

What is Ohm’s Law?

Answer 17

V = IR
V = voltage 
I = current
R = resistance

Question 18

What is the current in an open circuit?

Answer 18

Current is zero as there is no path for the current to flow.

Question 19

What happens when a circuit is short circuited?

Answer 19

Voltage is 0 and resistance is 0. 0 resistance results in and infinitely large current.

Question 20

What is the definition of electric power?

Answer 20

The rate per unit time at which electrical energy is transferred by an electrical circuit.

Question 21

What is the unit of power?

Answer 21

Watt (W)

Question 22

What is the formula for calculating power?

Answer 22

P = VI

Question 23

What is the formula for energy? What is the formula when power is constant?

Answer 23

E = ∫[t1-t2] p dt
when power is constant:
E = Pt

Question 24

For basic circuit analysis using Ohm’s law, under what circumstances must the result be multiplied by the negative?

Answer 24

When the current is moving from the negative end to the positive end, the result must be multiplied by negative 1.

Question 25

How can the formula for power be transformed to deal with current, resistance and voltage?

Answer 25

P = VI = (I²)(R) = (V²)/(R)