Download 5 - Circuits Notes Handout

10/08/2017
S30 Unit B: Physics - Circuit
Analysis
Name: __________
Date: __________
Parts of a simple circuit:
The Wire
- is the source of _____________ to move through the circuit
- is made of a conducting metal (often copper, sometimes gold)
- often wrapped in a plastic insulating coating to prevent _________ from _______________
from causing damage
- the amount of _____________ (electrons) flowing through the wire at any point per second is
called _____________
Current
Symbol = I
Units: Amps (A)
The units of current are defined as coulombs
per second (C/s) or amperes, named after the
19th century physicist Andre-Marie Ampere,
who is one of the first people (along with
Orsted) to link electricity and magnetism.
The Battery
- the source of _______________ in the circuit
- the battery gives energy to the electrons already present
in the wire, causing them to move.
- this energy is called ______________
Voltage
Symbol = V
Units: volts (V)
The unit of voltage is named after Alessandro
Volta who invented the first chemical battery.
The Resistor
- as current passes through any material, it loses some
energy to electrical resistance. This energy is typically
converted to __________.
Resistance
Symbol = R
Units: Ohms (____)
By using Volta's early battery, Ohm established the relationship between
_____________, _____________ and ________________:
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10/08/2017
Now, let's follow our electrons through the circuit and see what happens to them along the way.
1. The electrons in the wire are ___________ to the positive terminal of
the battery. They pass through the battery and gain ___________.
2. The electrons move through the resistor. They _____ energy.
Question: where does the energy of the electrons go?
If we want to calculate how much energy the electrons lost as they go through the resistor, we
can use Ohm's law.
3. The electrons have given their energy away to the resistor or device. They return to the battery
for more voltage, and the process continues.
ex) If a current of 2.0 A flows from a 30 V battery across a 10 Ω resistor, what voltage is found
before and after the resistor?
Parallel and Series Circuits
A Series Circuit
So far, we have only looked at series circuits. In a series, resistors are placed end-to-end so that
electrons must flow through each resistor.
Important Note:
Current is exactly the same everywhere in a series
circuit. The same amount of charge per unit of time
passes through each point, as there is nowhere else for
charge to go. However, the voltage will be different in
each resistor, as energy is lost due to heat in the
resistor.
A parallel circuit:
In parallel, electrons have more than one path to follow. The
resistors are not placed end to end, but parallel to one another.
Important Note:
Voltage is the same across each resistor in a parallel circuit,
as the electrons will split, some going across one resistor,
some across the other. All these electrons have the same
voltage.
The current, however, will differ as more electrons can go through a resistor with less resistance.
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10/08/2017
Measuring Current and Voltage in a Circuit
A voltmeter measures the difference in energy between two
points in a circuit, otherwise known as voltage.
In order to measure voltage, it has to be in ___________ to
the circuit. Why? Because it needs to measure a
______________ in energy between two points.
Check out this diagram. If the voltmeter was placed between
points A and B, it would measure electrons with the same
energy and give a reading of zero.
An ammeter measures the amount of charge per second that
passes by a point in a circuit (the current).
In order to measure current, it has to be in _________ to the
circuit. Why? Because it needs to measure _____ of the current
passing through a point, not just part of it.
Check out this diagram: if the ammeter was between points C
and D, it would only measure the number of electrons that take
that path, not the ones going through the resistor.
If it is in series (between A and B), it can catch all the electrons.
Practice: page 384 #7 and 8
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