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Dr Pusey
www.puseyscience.comQ: Write a definition for Current, Voltage and Resistance
Ohm’s Law Ohms law says that the Current
running through a circuit is controlled by the Voltage and the Resistance.
𝑉 = 𝐼 × 𝑅
𝐼 =𝑉
𝑅
𝑅 =𝑉
𝐼
I R
V
Ohms Law Quiz
I R
V
Voltage Current Resistance
0.5 A 4 Ω
6 V 4 Ω
8 V 2.0 A
10 V 4 Ω
12 V 3.0 A
V
A
Find the unknown values – Show your working out!
Ohms Law Quiz
I R
V
Voltage Current Resistance
4x0.5 = 2 V 0.5 A 4 Ω
6 V 6/4 = 1.5 A 4 Ω
8 V 2.0 A 8/2 = 4 Ω
10 V 10/4 = 2.5 A 4 Ω
12 V 3.0 A 12/3 = 4 Ω
V
A
Find the unknown values
The resistance of the resistor stayed the same! This means that it is “Ohmic”
“Ohmic” or “Non-Ohmic” All circuit components (even the wires) have a
resistance.
Ohmic (a): Resistance is the same, no matter what voltage is applied.
Examples: Most Resistors, Wire
Non-Ohmic (b): Resistance changes with voltage
Examples: Lights, Computers
Series circuits Current must flow through devices sequentially
Current only has one path to follow
Current is same at any point in the circuit
Total Voltage is split/shared across components
Extra components in series increases the resistance, which _________ the current.
If something breaks in a series circuit, the whole thing stops working.
Q: EXPLAIN WHY^^
Parallel circuit At least two different pathways for current to
travel
Current is shared between different pathways.
Total voltage across components is the same
Extra components draw more current.
E.g. New Christmas lights
Series and ParallelSeries Circuits Parallel
Extra components reduce the current Extra components increase the current
One broken component stops circuit One broken component has no effect
Requires less wiring Requires more wiring
A switch controls everything Multiple control points
Draws less power Draws more power
Components affect each other (adding more will affect how they perform)
Components are independent from each other.
Quick Quiz Draw circuits showing three lights controlled by one switch
(like Christmas lights). A) Draw the lights in series
B) Draw the lights in parallel
C) Would the lights be brighter in A, or B? Or are they the same brightness? Justify your reason
D) For each case, discuss what would happen to the brightness if you added another lamp.
Quick Quiz A) Draw the lights in series
B) Draw the lights in parallel
C) Would the lights be brighter in A, or B? Or are they the same brightness? Justify your reason
B, because each globe has a direct connection to the battery, so more current can circulate than in A
D) For each case, discuss what would happen to the brightness if you added another lamp.
In (A), they would go dimmer due to additional resistance
In (B), they wouldn’t change, because they are independent of each other
Short Circuits How?
When the normal pathway is cut short due to a conductor incorrectly connecting two points.
Note: Humans make excellent conductors – DANGER!
If a human is causing a short circuit, they will conduct the current, which causes an electric shock.
Other problems with short circuits: Sensitive components receive too much current and
stop working Overheating of batteries – KABOOOOOOM!
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