Download Ohms Law Notes

Introduction to circuits,
Coulomb Law.
Friday, March 10, 2017
Friday, 3/10
Unit: Circuits
1. What would life be like if we did not
have batteries?
2. What would you miss the most if you did
not have batteries?
Upcoming dates:
Note: you will have a HWK check or quiz each class
What is electric current?
 The
continuous flow of
electrons (electric
charge) through a
conducting metal.
 Current is the rate at
which the electrons
(energy); meaning it is
the energy per unit of
time
 I = ΔQ / Δt
 I = charge/s
What requirements are there in
order for current to exist?
A
source of electric potential energy which we
call voltage (V).

This is the source that gives the the charges energy
(volt = 1 Joule/coulomb).
the charges repel each
causing the charge to move

The charges need a conductive path; example
metal (metals are conductors) wire.
Relating current to what we
know about energy.
Types of current
Alternating Current
 Flow of current that periodically changes direction

Produced in power plants
 Current
from a wall outlet changes direction 120 times
per second
Direct Current
 The flow of current in one consistent direction

Examples
 Batteries
 Solar

cells
Current from a battery travels from the positive
terminal to the negative terminal.
Common Language
Quantity
Definition
Note Symbol
Taking
Guide
Potential
difference
current
resistance
Unit
Measuring
Device
Current
 The
continuous flow of electrons (electric
charge) through a conducting metal.
 Current is the rate at which the electrons
(energy); meaning it is the energy per unit of
time
 Measured in amperes (A)
 I = ΔQ / Δt
 I = charge/s
Ammeter
a device that measures current
attached in series
Potential difference
 Potential
difference (also voltage (V) can be
thought of as the force pushing electric charges
along a conductor. Voltage between two points
creates an electric field.



Measured in Volts (V)
V = UE /Q
(volt = 1 Joule/coulomb).
Voltmeter
a device that measures
electric potential difference,
must be connected in parallel
Resistance
 Resistance
(R) is a measure of how difficult it is to
push the charges along. The less difficult it is the
better conductor it is.
 The energy is transformed at the resistor
(potential energy is converted).
 Examples: light bulb, charging your phone, making
coffee, etc.

Measured in Ohms ()
 Resistance



is dependent on
The material which is measured by resistivity
The length of the conductor (more resistance for
greater length (L)
The width (the wider it is the lower the resistance (A)
Quantity
Definition
NoteSymbol
Taking
Guide
Unit
Measuring
Device
Potential
difference
V
Energy in the circuit
Volts
Voltmeter
current
I
Rate of flow
Amperes
Ammeter
resistance
R
Opposes current
OhmsΩ
Ohmmeter
Electrical Circuit Terminology
– a path that allows electricity to flow
 Circuit diagram – a simplified representation
of an electrical circuit that shows only the
electrical connections of elements in a circuit.
 We will study two types of circuits:
 Circuit


Series circuit
Parallel circuit
Electrical Circuit Terminology
Ohm’s Law
 Ohm's
Law analyzes the relationship between
voltage and current in an ideal conductor.
 Ohm's Law is given by:
V
= I * R
I = V/R
R = V/I
Example
A flashlight that is powered by 3 volts and uses a bulb
with a resistance of 60 ohms. What is the current
flowing through the circuit?
Practice
 Ohm’s
Law 1