Unit 2 About Physics: Electricity and Electronics, Slides of Engineering Physics

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In unit 2 we will learn about the physics of electricity and electronics.

This includes circuits, Ohm’s law, resistance, electrical energy and power, electromagnetism and electronic components.

What is

electricity?

What is inside an atom?

Thomson’s Plum pudding model

Rutherford model

Rutherford Bohr model

Charge cloud model

Quantum model of the nucleus

The atom

An atom is a fundamental unit of matter

made up of

protons (with a positive charge)

neutrons (neutral – no charge)

electrons (with a negative charge)

An atom will usually have the same number of positives and negatives This makes the atom NEUTRAL.

Proton (+)

Neutron

Electron (-)

Electrical Charge

Electric charge is given the symbol

Q

Electrons are the charge carriers

that flow in an electrical circuit –

from the negative to positive

terminals.

Electrical Charge

The charge on a proton is

1.6 x 10

• C

which is the same size as the charge on an

electron.

What is electricity?

Electrons have a negative charge

(Q) measured in coulombs (C).

Electrons move round a circuit from

negative to positive (remember like

charges repel, opposites attract)

giving rise to an electric current.

Conductors & Insulators

What makes something a good conductor?

Good conductors allow electrons to move

through them easily. Insulators do not

allow electrons to move easily.

Charge, Current & Time

Electric current is given the symbol

I

Electric current is the movement of

negative charges (electrons) in a

circuit

Charge, Current & Time

If current is charge flowing per second then

t

Q

I 

time in seconds (s)

Current in Amps (A)

Charge transferred in coulombs (C)

so a current of 1 A is 1 C of charge transferred in 1 s.

Charge, Current & Time

This can be rearranged as

or

Q  It

I

Q t 