ELECTRICITY

CHARGING BY FRICTION (FULL EXPLANATION + DIAGRAMS)

What it is

How to know who loses/gains?

Use the Triboelectric Series (given on test).

• Higher on list → loses electrons → becomes positive

• Lower on list → gains electrons → becomes negative

🔵 DIAGRAM: Charging by Friction

(Neutral objects → rubbed → one becomes +, one becomes –)

Before rubbing

Both objects neutral:

Code

Object A:  +  -  +  -  +  -
Object B:  +  -  +  -  +  -

During rubbing

Electrons move from the material HIGHER on the series → LOWER on the series.

Example: Glass (higher) rubbed with plastic wrap (lower)

Code

Glass:      +  -  +  -  +  -   → loses electrons
Plastic:    +  -  +  -  +  -   → gains electrons

After rubbing

Code

Glass:      +  +  +  +  +      (POSITIVE)
Plastic:    -  -  -  -  -      (NEGATIVE)

CHARGING BY CONTACT?

• Negative object = has extra electrons

• Positive object = has too few electrons

• Neutral object = equal electrons & protons

When they touch, electrons move to fix the imbalance.

⚡ TWO CASES

We do BOTH with diagrams.

🔵 CASE 1 — NEGATIVE OBJECT TOUCHES NEUTRAL

(Electrons move into the neutral object)

Before contact

Code

NEGATIVE OBJECT:   - - - - - + + +
NEUTRAL OBJECT:    + - + - + -

During contact

Electrons flow from negative → neutral.

Code

NEGATIVE OBJECT:   - - - - + + + +
NEUTRAL OBJECT:    - - - - + - + -

After contact

Code

NEGATIVE OBJECT:   still negative
NEUTRAL OBJECT:    becomes negative

✔ Neutral becomes negative
✔ Electrons moved INTO it

🔴 CASE 2 — POSITIVE OBJECT TOUCHES NEUTRAL

(Electrons move out of the neutral object)

Before contact

Code

POSITIVE OBJECT:   + + + + - - -
NEUTRAL OBJECT:    + - + - + -

During contact

Electrons flow from neutral → positive.

Code

POSITIVE OBJECT:   + + + - - - - -
NEUTRAL OBJECT:    + + + - + -

After contact

Code

POSITIVE OBJECT:   still positive
NEUTRAL OBJECT:    becomes positive

✔ Neutral becomes positive
✔ Electrons moved OUT of it

⚡ SUPER SIMPLE SUMMARY

• Touch with negative → electrons go into neutral → neutral becomes negative

• Touch with positive → electrons go out of neutral → neutral becomes positive

CHARGING BY INDUCTION

🧠 WHAT IS INDUCTION? (Proper explanation)

From your notes:

Meaning:

✔ The charged object NEVER touches

✔ Electrons inside the neutral object shift positions

✔ The object stays overall neutral

✔ The charge is temporary (only exists while the charged object is near)

This is the KEY difference from contact.

⚡ WHY DOES INDUCTION HAPPEN?

Because electrons move away from negative
and move toward positive.

Electrons are like scared little boiis:

• They run away from negative charges

• They run toward positive charges

So when a charged object comes close, electrons inside the neutral object rearrange.

🔵 CASE 1 — NEGATIVE OBJECT NEAR A NEUTRAL OBJECT

(Electrons get pushed away)

Before

Neutral object = electrons evenly spread.

During induction

Negative rod repels electrons → they move to the far side.

Result

• Near side becomes positive

• Far side becomes negative

• Object is STILL neutral overall

• Charge disappears when rod is removed

🔴 CASE 2 — POSITIVE OBJECT NEAR A NEUTRAL OBJECT

(Electrons get pulled toward the rod)

Before

Neutral object = electrons evenly spread.

During induction

Positive rod attracts electrons → they move to the near side.

Result

• Near side becomes negative

• Far side becomes positive

• Object is STILL neutral overall

• Charge disappears when rod is removed

1. PITH‑BALL ELECTROSCOPE

A tiny ball made of pith (light, non‑conductive material) hanging from a thread.

✔ HOW IT WORKS

The pith ball is neutral at the start.

A) Charged object brought NEAR (induction)

• Electrons inside the pith ball shift

• The pith ball becomes temporarily polarized

• It gets attracted to the charged object

B) Charged object TOUCHES the pith ball (contact)

• Electrons transfer

• The pith ball becomes charged

• Now it can repel from the same charge

✔ EXAMPLE: Negative balloon near pith ball

• Balloon repels electrons inside the pith ball

• Near side becomes positive

• Pith ball is attracted

✔ EXAMPLE: Negative balloon touches pith ball

• Electrons move into pith ball

• Pith ball becomes negative

• Now it repels from the balloon

2. METAL‑LEAF ELECTROSCOPE

This one is more sensitive and shows charge using two thin metal leaves.

✔ HOW IT WORKS

Inside the electroscope:

• A metal knob

• A metal rod

• Two thin metal leaves

All connected → electrons can move freely.

✔ WHAT HAPPENS WHEN A CHARGED OBJECT COMES NEAR?

A) Induction (NO touching)

• Electrons shift inside the electroscope

• Leaves get the same charge

• Leaves repel and spread apart

B) Contact (TOUCHING)

• Electrons transfer

• Electroscope becomes charged

• Leaves stay apart even after the rod is removed

🧠 KEY IDEA

Leaves spread apart = electroscope is charged.
Leaves collapse = electroscope is neutral.

PART 1 — CIRCUITS (SERIES + PARALLEL)

🔵 SERIES CIRCUIT

Only ONE path for electrons.

Rules

• Current is the SAME everywhere
  IT = I1 = I2 = I3

• Voltage SPLITS
  VT = V1 + V2 + V3

• Resistance ADDS
  RT = R1 + R2 + R3

• If one bulb breaks → ALL go out

🔴 PARALLEL CIRCUIT

Electrons have multiple paths.

Rules

• Voltage is the SAME on each branch
  VT = V1 = V2 = V3

• Current SPLITS
  IT = I1 + I2 + I3

• Resistance DECREASES
  1/RT = 1/R1 + 1/R2 + 1/R3

• If one bulb breaks → others stay on

PART 2 — OHM’S LAW (V = IR)

Using GRASP properly

Formula

• V = I × R

• I = V ÷ R

• R = V ÷ I

✔ Example 1 — Find Voltage (V)

A current of 4 A flows through a 40 Ω resistor.

G: I = 4 A, R = 40 Ω

R: V

A: V = IR

S: V = 4 × 40 = 160 V

P: The voltage is 160 V.

✔ Example 2 — Find Resistance (R)

V = 240 V, I = 20 A

G: V = 240 V, I = 20 A

R: R

A: R = V ÷ I

S: 240 ÷ 20 = 12 Ω

P: The resistance is 12 Ω.

✔ Example 3 — Find Current (I)

V = 30 V, R = 15 Ω

G: V = 30 V, R = 15 Ω

R: I

A: I = V ÷ R

S: 30 ÷ 15 = 2 A

P: The current is 2 A.

Current (I)

⚡ SUPER SUMMARY TABLE