Transcript Circuits, Volts, Amps, Ohms

Circuits, Volts, Amps,
and Resistance
Series circuits
Simple circuits that have only one path for
the current to flow are called series
circuits.
Series circuits can be compared to that of
a race track.
Parallel Circuits
Parallel circuits are circuits that allow
electricity to flow in multiple paths.
Parallel circuits are more like city streets
than a race track. They give the electricity
options for movement.
The Battery
Batteries contain stored electric potential
energy from chemical reactions that go on
inside the battery.
A good example of the reaction is:
Zn + Cu 2+ = Zn 2+ + Cu
The battery provides the potential energy
to do “work”
In order to do this “work” the battery must
be connected in a closed circuit
Energy is measured in “Joules”
The energy that is stored in the battery is
also measured in Joules.
Potential energy difference is measured in
Joules per Coulomb or Volts.
Therefore:
V=E
Q
So
Potential energy difference =
the amount of stored energy
charge
We can measure potential energy
difference using a voltmeter. The
measure is in volts.
V
The voltmeter must be put in parallel with
the circuit.
This means it must create it’s own
separate loop in the circuit to work
properly.
The voltmeter will measure the difference
at one point on the circuit and compares it
to another point on the circuit.
The Ammeter
An ammeter measures current through the
circuit. It measures amps
Think about current as the speed that the
charges travel, an ammeter is like a speed
radar gun for electricity.
A
An ammeter must be put in series to work
properly.
Resistance
What does it mean to “resist”?
What would be harder?
1. Pushing a 50kg box across carpet?
2. Pushing a 50kg box across tile floors?
Resistance is the property of a substance
to hinder motion.
A resistor converts electric energy into
other forms of energy (heat, light)
Resistance is the ratio of potential energy
difference (voltage) across a load, to the
current through the load
Resistance = Voltage
Current
Resistance is measured in Ohms or Ω
Ohm’s Law
This equation is referred to as Ohm’s Law
Where V = IR
V
R
I
If we had a voltmeter and a
ammeter we could measure the
resistance
Example Question
What is the resistance of the heating coil of an
electric heater, if a current of 12.5A runs through
it, when connected to a wall outlet of 120V?
Given:
Solution:
Paraphrase:
Example Question
What is potential difference (voltage) across a light
bulb that has a resistance of 3ohms and a
current of 1.5A
Given:
Solution:
Paraphrase:
Factors that effect resistance
1. Length – resistance increases with
length
2. Cross sectional area – resistance
decreases when area increases
3. Temperature – resistance increases
when temperature decreases
4. Material – some metals allow electrons
to move more freely than others
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In your own words explain electrical resistance.
What is the formula for resistance and what units are
equivalent to the ohm?
List 3 characteristics of a wire that affect its resistance.
A light bulb passes a current of 0.83 A when the
potential difference is 120V. What is the bulb’s
resistance?
What is the potential difference across an electric
water heater element that has a resistance of 32ohms
when a current through it is 6.8 A?
Matt says that if the resistance of a load becomes
larger, the current must become larger as well.
Melissa explains that the current should decrease.
Who is correct? Explain.