Chapter 8 – Static Electricity (Class 7, Maharashtra Board)

Chapter 8: Static Electricity

Class 7 • Maharashtra Board General Science Mobile-friendly • Proper line gaps • Colourful & neat

1) 20 Important Words & Meanings (Meanings in Hindi)

Static Electricityरगड़/इंडक्शन से बना स्थिर विद्युत आवेश।

Electric Chargeकणों का गुण जो आकर्षण/अपसारण कराता है।

Positive Charge (+)ऋण आवेश की कमी होने पर बना धन आवेश।

Negative Charge (−)अतिरिक्त इलेक्ट्रॉन होने से बना ऋण आवेश।

Neutralधन और ऋण आवेश बराबर — शुद्ध आवेश शून्य।

Frictionरगड़ जिसके कारण इलेक्ट्रॉनों का स्थानांतरण होता है।

Attractionविपरीत आवेश एक-दूसरे को खींचते हैं।

Repulsionसमान आवेश एक-दूसरे को दूर धकेलते हैं।

Conductorजहाँ आवेश आसानी से बहता है (जैसे ताँबा)।

Insulatorजहाँ आवेश आसानी से नहीं बहता (जैसे प्लास्टिक)।

Inductionपास के आवेश के कारण बिना छुए आवेश उत्पन्न होना।

Conductionसंपर्क से आवेश का स्थानांतरण।

Electron ($e^-$)ऋण आवेशित सूक्ष्म कण।

Proton ($p^+$)धन आवेशित सूक्ष्म कण।

Atomद्रव्य का सूक्ष्मतम कण — सामान्यतः विद्युत तटस्थ।

Electroscopeयंत्र जो आवेश की उपस्थिति दर्शाता है।

Lightningमेघों में विशाल स्थिर आवेश का तेजी से धरती की ओर प्रवाह।

Lightning Conductorताँबे की पट्टी/अर्थिंग से भवन को बिजली गिरने से सुरक्षा।

Earthingआवेश को सुरक्षित रूप से जमीन में बहा देना।

Moist Airनमी वाली हवा जो स्थिर आवेश को जल्दी समाप्त कर देती है।

2) Important Notes (Quick Revision)

All matter is made of atoms which are electrically neutral (equal positive and negative charge). Rubbing transfers some negative charges (electrons), creating imbalance → objects become charged.
Like charges repel and unlike charges attract. Repulsion is a sure test for charge.
Methods of charging: (i) Friction (rubbing), (ii) Conduction (contact), (iii) Induction (no contact; temporary unless earthed).
Static charge stays on surfaces; gets lost quickly in moist air or on conductors (by earthing).
Electroscope: gold leaves diverge when charge is present; touching the disc discharges via your body to earth.
Lightning: huge charge separation in clouds; discharge to ground produces light, heat, sound. A lightning conductor (copper strip to buried iron plate with coal & salt and watering provision) safely conducts charge to earth.
Safety: During lightning—go indoors, avoid tall isolated trees/open fields/metal objects/water; unplug appliances; crouch low if caught outside.

Concept	Key idea	Example / Note
Frictional electricity	Charge produced at rubbing surface; stays briefly	Comb rubbed on hair attracts paper bits
Induction	Charge separation in nearby neutral object	Charged comb bends a thin water stream
Conductor vs Insulator	Conductors let charge move; insulators hold it	Copper (conductor), plastic balloon (insulator)
Test for charge	Repulsion confirms like charges	Two similarly charged straws move apart

3) 20 Important “One-Word Answer” Type Questions

Which charge do electrons carry?
Negative (−).
A neutral object has equal amounts of?
Positive and negative charge.
Like charges show _____.
Repulsion.
Unlike charges show _____.
Attraction.
Name the charge developed on glass rubbed with silk.
Positive (on glass).
Name the device to detect charge.
Gold-leaf electroscope.
What is the sure test of charge—attraction or repulsion?
Repulsion.
Charging without contact is called?
Induction.
Charging by touch is called?
Conduction (contact).
Which material becomes easily charged—plastic or copper?
Plastic.
Device that protects buildings from lightning.
Lightning conductor.
Which metal strip is used in a lightning conductor?
Copper.
What quickly removes static charge from bodies?
Moist air / earthing.
Greek name ‘elektron’ refers to?
Amber.
Scientist who named charges + and −.
Benjamin Franklin.
Metal used for thin leaves in an electroscope.
Gold.
Type of electricity produced by rubbing.
Frictional (static) electricity.
Which force acts between charges?
Electrostatic force.
A balloon sticks to a wall due to?
Induction & attraction.
What is the state of charge flow in static electricity?
It does not flow; it stays localized.

4) 20 Very Short Answer Questions (1–2 lines)

Why does a comb attract paper bits after rubbing on dry hair?
Rubbing transfers electrons to the comb; induced opposite charge in paper causes attraction.
Why are static experiments better in winter?
Air is drier; moisture otherwise leaks charge away.
What happens to electroscope leaves when a charged body is brought near?
They diverge (repel) due to like charges appearing on both leaves.
What is meant by earthing?
Providing a safe path for charge to flow into the ground.
Why don’t metals hold charge by rubbing?
Free electrons move; charges quickly flow away (especially if earthed).
State one use of induction in daily life.
Balloon sticking to wall; charged comb bending water stream.
What is the sign of charge on silk after rubbing with glass?
Negative (it gains electrons).
Which is the safer place during lightning—inside car or under a lone tree?
Inside a car (Faraday cage effect); never under a lone tree.
What makes a lightning conductor effective?
Sharp top, low-resistance copper path to deep earthing with coal, salt, and water.
Why does a charged object attract a neutral one?
Induced charge separation creates net attraction.
What brings the leaves of an electroscope together again?
Discharging by touching (earthing) or moist air.
Do like charges ever attract?
No; like charges always repel.
Which gas formation after lightning helps soil fertility?
Nitrogen oxides dissolve in rain and add nitrogen to soil.
Why should we unplug electronics during thunderstorms?
Surges from lightning can damage devices.
What is the simplest test to identify a charged straw?
Bring it near another similarly charged straw—repulsion confirms charge.
Why does polyester curtain cling to you?
Rubbing causes charging; opposite charges attract.
What is meant by ‘static’ in static electricity?
Charge stays localized; it doesn’t continuously flow like current.
Name one insulator and one conductor used here.
Insulator: plastic/balloon; Conductor: copper.
Do we see lightning every rainy day?
No; only when strong charge separation develops in clouds.
Why do we use gold leaves in an electroscope?
Gold is very thin, malleable and doesn’t oxidize easily—responds to tiny charges.

5) 20 Short Answer Questions (2–3 lines)

Explain how rubbing produces charge on two objects.
Rubbing transfers electrons from one surface to the other. The donor becomes positive (electron deficit), the receiver becomes negative (electron excess).
Why is repulsion a sure test of charge?
Attraction can occur with neutral objects (induction), but repulsion only occurs between like-charged bodies—confirming both are charged similarly.
Describe charging by conduction.
A charged object touches a conductor and transfers charge; after separation, both carry similar type of charge (typically reduced in magnitude).
Describe charging by induction.
A charged body brought near a conductor separates charges; earthing one side and removing the cause leaves a net charge without contact.
Why does a comb bend a thin stream of water?
The charged comb induces opposite charge on the nearer side of the polar water molecules—net electrostatic attraction bends the stream.
State two differences between conductors and insulators.
Conductors allow charge movement (low resistance) and discharge quickly; insulators trap charges on their surfaces and keep them for longer.
How does moist air reduce static effects?
Water molecules provide a conductive path for charges to leak away into air and nearby objects (natural earthing).
What happens inside a gold-leaf electroscope when charged?
Both leaves get the same type of charge and repel each other, so they diverge; touching discharges them and they collapse.
State two safety rules during lightning.
Stay indoors and away from windows/metal; avoid tall isolated trees, water bodies, and using wired devices.
Why is the top of a lightning conductor pointed?
A sharp tip concentrates electric field and helps leak charge gradually to air/collect it efficiently, guiding discharge safely to earth.
Why are coal and salt added to the earthing pit?
They retain moisture and lower earth resistance, helping charges spread quickly into the ground.
What is the role of the buried iron plate in lightning protection?
It enlarges contact with the moist soil, providing a broad low-resistance path for charge dissipation.
Why is a plastic balloon better than a metal ball for static experiments?
Plastic is an insulator; it holds charge on its surface longer, whereas metal discharges quickly (especially if earthed).
State two atmospheric benefits from lightning.
Formation of nitrogen oxides (fertility to soil) and ozone (helps absorb harmful UV radiation).
What do you observe when two similarly charged straws are brought close?
They repel each other and move apart—evidence of like charges.
How does a charged balloon stick to a wall?
It induces opposite charges on the wall’s surface; attraction keeps it stuck until charge leaks away.
Why should you not stand under a lone tree during a storm?
Tall, isolated objects can attract lightning; current may pass through trunk & ground, endangering people nearby.
Explain why a rubbed tubelight glows faintly in darkness.
Static charges can cause small discharges that excite gas inside the tube, producing faint light.
How do we safely discharge a charged electroscope?
Touch the metal disc with your hand (or connect to earth) so charge flows to the ground; leaves collapse.
Why is plastic comb better than wet comb for attracting paper?
Water on a wet comb provides a leakage path; charge doesn’t stay, so attraction weakens.

6) Textbook Exercise – Perfect Answers

Q1) Choose the correct option and fill in the blanks.

(a) There is always repulsion between like charges.
(b) Displacement of negative charge is responsible for generation of electric charge in an object (electrons transfer on rubbing).
(c) A lightning conductor is made of a copper strip.
(d) Copper does not get electrically charged easily by rubbing (metal = conductor).
(e) There is always attraction when opposite electric charges come near each other.
(f) A charged object can be detected with an electroscope.

Q2) Explain why it is not safe to go out with an umbrella when there is heavy rain, lightning or thunder.

The metal parts and pointed tip of an umbrella can act as an easy path for lightning; rainwater increases conductivity. Holding it raises you as a “tall object,” increasing strike risk.

Q3) Answer in your own words.

(a) How will you protect yourself from lightning? Stay indoors; avoid using wired devices; keep away from doors/windows/metal; if outside, avoid lone trees, water, and open fields; crouch low with feet together; do not lie flat.

(b) How are charges generated? By rubbing (friction), electrons shift between surfaces; by conduction (touch), charge is shared; by induction (nearby charge), separation occurs without contact.

(c) In a lightning conductor, how is electricity spread into ground? Through a low-resistance copper strip connected to a deep earthing system: a cast-iron plate in a pit filled with coal and salt and kept moist for good conductivity.

(d) Why do farmers stick an iron staff into the ground in rainy conditions? The staff works like a simple lightning conductor, providing a preferred path to earth so charge does not pass through people nearby (one should keep distance from the staff).

(e) Why is lightning not seen every day during the rainy season? Strong charge separation in clouds needs specific conditions (updrafts, ice/water collisions, dryness aloft); these don’t occur daily.

Q4) What are the characteristics of a static electric charge?

Produced by friction/induction; remains localized on surfaces; leaks off through moist air or earthing; like charges repel, unlike attract; can induce charge separation in nearby objects; detected by electroscope; exists briefly compared to current electricity.

Q5) What damage is caused by lightning? How will you create awareness to prevent it?

Damage: Fires, structural damage to buildings/trees, power surges destroying appliances, injury or death to people/animals.

Awareness: Poster campaigns, school demos on lightning safety, installing lightning conductors on tall buildings, sharing “30–30 rule,” broadcasting alerts, training to unplug devices and to avoid tall isolated trees/open fields during storms.

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8. Static Electricity