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!

Safety Fuses - Safety for the circuit and humans

Fuses are simply a special wire, connected in series

If the wire receives more current than it’s supposed to, it will melt away and there will be no pathway for electricity to flow: