Electricity: Basics

Question 1

What is the definition of an electric current?

Answer 1

An electric current is the rate of flow of charge past a point in a circuit.

Question 2

What is current measured in and what is it’s state symbol?

Answer 2

Current is measured in Ampere’s (A) and it’s symbol is I.

Question 3

What is charge measured in and what is it’s state symbol?

Answer 3

Charge is measured in Coulombs (C) and it’s symbol is Q

Question 4

What charge does one electron carry?

Answer 4

1.6 x 10⁻¹⁹ C

Question 5

What charge does one proton carry?

Answer 5

1.6 x 10⁻¹⁹ C

Question 6

What is charge?

Answer 6

Charge is a property carried by some particles.

Question 7

What’s an ammeter?

Answer 7

An ammeter is a device used to measure current in a circuit.

Question 8

How do we calculate charge?

Answer 8

Q = I x T

Question 9

What is the definition of potential difference?

Answer 9

The work done per unit charge

Question 10

How do we connect ammeters into a circuit?

Answer 10

In series.

Question 11

How do we connect voltmeters into a circuit?

Answer 11

In parallel.

Question 12

How do we calculate voltage? (without resistance)

Answer 12

V = W / Q

Question 13

What is the definition of resistance?

Answer 13

R = V / I

Question 14

What is resistance?

Answer 14

Opposition to the flow of charge.

Question 15

What is Ohm’s Law?

Answer 15

For a metallic conductor at a constant temperature, the current is directly proportional to the potential difference? Alternatively, this can be shown as V = I x R

Question 16

What does the graph of an Ohmic Resistor on an I - V graph look like?

Answer 16

A straight line that goes through the origin where the gradient remains constant.

Question 17

What does the graph of a filament lamp on an I - V graph look like?

Answer 17

A straight line that goes through the origin until it starts to curve at both ends and flattens out.

Question 18

What does the graph of a diode on an I - V graph look like?

Answer 18

A flat line that goes through the origin and goes upwards sharply once it has reached the threshold.

Question 19

Why does the graph of an Ohmic Resistor look the way it does?

Answer 19

The resistance is constant so the gradient doesn’t change.

Question 20

Why does the graph of a filament lamp look the way it does?

Answer 20

As the current increases, the filament heats up causing vibrations in the metal ions. This increases the chance that electrons will hit the metal ions which increases resistance lowering the gradient on the graph.

Question 21

Why does the graph of a diode look the way it does?

Answer 21

Below a threshold P.D. the resistance is infinite so no current flows. Above the threshold P.D. there is very little resistance so the gradient is very steep.

Question 22

What is a conductor that follows Ohm’s law called.

Answer 22

An Ohmic Conductor

Question 23

What is a conductor that doesn’t follows Ohm’s law called.

Answer 23

A Non Ohmic Conductor