1. Unit 2 | Using tools, equipment and other devices
Lecturer: Mr. Jerome Smith
Course: CAP

2. Basic Electric Circuits & Components
Introduction
SI Units and Common Prefixes
Electrical Circuits
Direct Currents and Alternating Currents
Resistors, Capacitors
Ohm’s, Power Law
Power Dissipation in Resistors
Resistors in Series and Parallel
Resistive Potential Dividers
Sinusoidal Quantities
Circuit Symbols

3. SI Units Quantity Quantity symbol Unit Unit symbol Capacitance C Farad
Charge Q
Coulomb
Current I
Ampere A
Electromotive force E
Volt V
Frequency f
Hertz Hz
Inductance (self) L
Henry H
Period T
Second s
Potential difference
Power P
Watt W
Resistance R
Ohm Ω
Temperature
Kelvin K
Time t

4. Common Prefixes Prefix Name Meaning (multiply by) T tera 1012 G giga
109 M
mega
106 k
kilo
103 m
milli
10-3 
micro
10-6 n
nano
10-9 p
pico
10-12

5. Electrical Circuits Electric charge Electric current
an amount of electrical energy
can be positive or negative
Electric current
a flow of electrical charge, often a flow of electrons
conventional current is in the opposite direction to a flow of electrons
Current flow in a circuit
a sustained current needs a complete circuit
also requires a stimulus to cause the charge to flow

6. Section 7.2: Electric Current
Static Electricity: build up of charges that pass QUICKLY to another object
Electric Current: continuous flow of charges through a conductor

7. Electromotive force and potential difference
the stimulus that causes a current to flow is an e.m.f.
this represents the energy introduced into the circuit by a battery or generator
this results in an electric potential at each point in the circuit
between any two points in the circuit there may exist a potential difference
both e.m.f. and potential difference are measured in volts

8. A simple circuit
A water-based analogy

9. Voltage Voltage is created by
a chemical cell (battery) when it changes chemical energy to electrical energy
by a generator when it changes mechanical energy to electrical energy
by a solar cell when it changes light energy to electrical energy.

10. Direct Current and Alternating Current
Currents in electrical circuits may be constant or may vary with time
When currents vary with time they may be unidirectional or alternating
When the current flowing in a conductor always flows in the same direction this is direct current (DC)
When the direction of the current periodically changes this is alternating current (AC)

11. Resistors, Capacitors and Inductors
Resistors provide resistance
they oppose the flow of electricity
measured in Ohms ()
Capacitors provide capacitance
they store energy in an electric field
measured in Farads (F) Forumlae:
Capacitors in Series: (1/CTOTAL) = (1/C1) + (1/C2) + (1/C3) Capacitors in parallel: CTOTAL = C1 + C2 + C3 .....
Inductors provide inductance
they store energy in a magnetic field
measured in Henry (H)

12. Check for Understanding
What is voltage?
How is voltage generated? (3 ways)
What is current?

13. Resistance
Resistance: the tendency for a material to oppose the flow of electrons
Changes electrical energy into thermal energy and light
Ex: lightbulb filament
Resistance is measured in Ohms (Ω)

14. What Affects Resistance?

15. Household Circuits:
Fuse: a small piece of metal that melts if the current becomes too high Circuit Breaker: contains a small piece of metal that bends when it gets hot bending causes a switch to flip and opens the circuit

16. Ohm’s Law
The current flowing in a conductor is directly proportional to the applied voltage V and inversely proportional to its resistance R
V = IR
I = V/R
R = V/I

17. Power Law Power is the measure of how much work can be done in
a given amount of time.
Did you know? 1. W = V x I 2. W = I2 x R ? 3. W = V2 / R ?
Lets see!!

18. Sinusoidal Quantities
Length of time between corresponding points in successive cycles is the period T
Number of cycles per second is the frequency f
f = 1/T

19. Circuit Symbols

21. Key Points

22. Let’s Compare Series and Parallel Circuits
Series Circuits
Parallel Circuits
_______ path(s) for current
Current ________________
Voltage ________________
Break in circuit _______________________
Adding resistance in series ______________________
_______ path(s) for current
Current ________________
Voltage ________________
Break in circuit _______________________
Adding resistance in parallel _______________________

23. Let’s Compare Series and Parallel Circuits
Series Circuits
Parallel Circuits
1 path(s) for current
Current is the same at every point
Voltage drops at each resistor
Break in circuit stops all current
Adding resistance in series decreases total current (dimmer light bulbs)
multiple path(s) for current
Current can be different in each branch
Voltage same across each resistance
Break in circuit does not affect other bulbs
Adding resistance in parallel increases total current