Download Ohm’s Law

Ohm’s Law
PSSA Requirement
Unit 9
Honors Physics
A look at electricity
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Static Electricity
Charges are stationary
(mostly)
Look at force between
charges
Electric field around
charged particles
Potential from a
charged particle
Current Electricity
• Charges are moving
(flowing)
• Look at how circuits
work
• Resistance to the flow
A New Language
• Quantities
– Current (unit - Amperes (A)
– Voltage (unit - Volt (V))
– Resistance (unit - Ohms (Ω))
• Option - Z gives Ω Symbol
Electric Current
Q
I
t
Current is defined as
the rate at which
charge flows past a
given point
Unit of Current: A (ampere) = C / s
Current and Flow
• Either positive or negative particles can
flow
• Conventional Current - direction positive
charge would flow
Microscopic View of Current
Circuit Requirements
• Circuit - complete path of conductors for
electrons (closed loop)
• Battery - Power Source - pushes electrons
around
• Something to use the current - light bulb
• Switch
Circuits
Measuring Current and Voltage
• Ammeter - measures current
– Must be placed in series (in line) with object it
is measuring
• Voltmeter - measures potential difference
between two points in a circuit
– Must be placed in parallel (around) the object it
is measuring
• Multimeter - Can measure more than 1
quantity
Voltage and Current
• When a voltage is applied to a conductor current is proportional to the applied
voltage
• Proportionality Constant is called
Resistance
I  V
V  IR
Resistance / Ohm’s Law
V
R
I
Units - Ω (ohms)
Ohm’s Law Notes
• Georg Simon Ohm (1787 - 1854) studied
electrical resistance
• ∆V = I R
• ∆V is the potential drop across the resistor
• Ohm’s Law is only valid for certain
materials - ohmic materials
Ohmic and Non-Ohmic Materials
Ohm’s Law Problems
An iron carries a current of 6.4
A when connected to a 120 V
source. What is the resistance
of the steam iron?