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REET Level 2 · Science

Electric Current: Static Charge, Ohm's Law, Circuit Safety and Effects of Current — REET Science Notes

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This page covers charge produced by rubbing, the basic quantities and formulas of electric current, series-parallel arrangement, short circuits and fuses, and the heating, magnetic and chemical effects of current, at the Class 6-8 NCERT level. REET 2024 carried 3 questions from this area, on static electricity and circuit safety.

  • 3 questions in REET 2024
  • Class 6-8 level
  • 9 min read
Verified 17 September 2026 · Source: NCERT Class 7 Science (Curiosity) — Chapter 3: Electricity: Circuits and their Components

How REET asks this topic

REET 2024 carried 3 questions from this topic: current rising sharply in a short circuit, and two questions on static electricity — rubbing a glass rod with silk gives it a positive charge, and a statement-based question on 'a plastic straw rubbed with polythene becomes negatively charged'. In other words, REET treats 'electricity' broadly — static charge, circuits, Ohm's law, safety (fuses, short circuits) and the effects of current. The level is NCERT Class 6-8, though knowing Class 10's I = V/R helps in reasoning out the causes.

Charge and static electricity

Matter is made of atoms, which contain positively charged protons and negatively charged electrons. Under normal conditions, an object stays neutral. When two objects are rubbed together, some electrons transfer from one to the other: the object that loses electrons becomes positively charged, and the one that gains them becomes negatively charged. This charge produced by rubbing is called static charge, because it does not flow on its own.

Like charges repel each other and unlike charges attract. A glass rod rubbed with silk becomes positively charged, while the silk becomes negatively charged; a plastic straw rubbed with polythene becomes negatively charged (NCERT Class 8). This is why two charged straws push each other away, while a charged straw is pulled toward a charged glass rod. Note that attraction can also happen toward a neutral object (a comb picks up bits of paper), so the sure sign of charge is repulsion, not attraction.

The instrument used to check whether an object carries a charge is the electroscope — when a charged object touches it, its metal leaves receive the same charge and spread apart. Sending charge from an object into the earth is called earthing. Lightning is an electrical discharge that happens between charges built up within clouds, or between a cloud and the earth; a lightning conductor fitted on tall buildings safely channels this charge into the ground.

Electric current — the basic quantities

Electric current (I)
the rate of flow of charge: I = Q / t; SI unit ampere (A); measured with an ammeter (connected in series in the circuit)[Source 2]
Charge (Q)
SI unit coulomb (C); 1 A = 1 C/s[Source 3]
Potential difference (V)
SI unit volt (V); measured with a voltmeter (connected in parallel)[Source 2]
Direction of current
by convention, from the positive (+) terminal of the cell to the negative (-); electrons flow in the opposite direction[Source 2]
Ohm's law
at constant temperature, V = IR; the unit of resistance R is the ohm (Ω)[Source 2]
What resistance depends on
directly proportional to the conductor's length, inversely proportional to its cross-sectional area, and dependent on the material and the temperature[Source 2]
Series arrangement
R = R1 + R2 + ...; the same current flows through all components[Source 2]
Parallel arrangement
1/R = 1/R1 + 1/R2 + ...; the same potential difference is across all components — household wiring uses this arrangement[Source 2]
Power and energy
P = VI (watt); the commercial unit is the kilowatt-hour: 1 kWh = 3.6 × 10^6 J (one 'unit' on an electricity bill)[Source 2]

Circuits, cells and safety

A cell has two terminals; in a circuit symbol, a long thin line represents the positive terminal and a short thick line the negative terminal. A combination of two or more cells is called a battery. A dry cell used in a torch supplies about 1.5 V. Current flows only when the circuit is closed; turning the switch 'ON' completes the circuit. Materials through which current flows easily are called conductors (copper, aluminium, the human body, salty water), and those through which it does not are insulators (rubber, plastic, dry wood, glass).

A short circuit happens when the insulating covering wears out and the live and neutral wires touch directly. Since the circuit's resistance drops to nearly zero, the current rises sharply according to I = V/R, the wire heats up excessively, and this can cause a fire. Overloading happens when too many appliances are run from a single socket, pushing the current beyond the safe limit. To guard against both, a fuse is fitted — a thin wire of a low-melting-point material that melts and breaks the circuit when the current exceeds a set limit. Fuses have largely been replaced today by MCBs (miniature circuit breakers), which switch off automatically when current exceeds the limit. Always buy electrical appliances that carry the ISI mark.

Effects of electric current

EffectPrincipleUse / example
HeatingCurrent flowing through a resistance produces heat: H = I²Rt (Joule's law)Heaters, irons, geysers (nichrome wire); a bulb's filament (tungsten — high melting point); fuses
MagneticA compass needle placed near a current-carrying wire is deflected — discovered by Hans Christian OerstedElectromagnets, electric bells, cranes that lift iron, motors
ChemicalA chemical change occurs when current passes through a conducting solution — gas bubbles at the electrodes, metal deposition, colour changeElectroplating: chromium on bicycle handles/car parts, tin on iron cans, purification of copper

CFL and LED tube lights waste less energy as heat compared with a filament bulb, which is why they save electricity.[Source 1]

How electroplating works

The NCERT Class 8 activity: place two copper plates in a copper sulphate solution and connect them to a battery. After some time, the plate connected to the negative terminal of the battery gains a layer of copper, while the plate connected to the positive terminal becomes thinner — copper from the solution deposits at the negative electrode, and an equal amount dissolves from the positive electrode into the solution. Coating an object with a desired metal using electric current is called electroplating.

Most liquids that conduct electricity are solutions of acids, bases and salts. Distilled water is a weak conductor of electricity, but dissolving a little salt in it makes it a conductor; tap water conducts because of the salts dissolved in it. To detect weak conduction, an LED is used in place of a bulb in a tester, because it lights up even at very low current.

How to teach this to children

Activity: finding conductors and insulators (Class 6)

Build a simple tester from a cell, a bulb, wires and two open ends. Have children test a key, a rubber band, a pencil lead (graphite), a coin, a plastic scale, water and so on, and fill in a table. Finding that graphite conducts is usually a fun 'surprise' for children.

Experiment: static charge

Rub two plastic straws with polythene, hang one from a thread and bring the other close (repulsion); then bring a glass rod rubbed with silk close (attraction). Children can also build a simple electroscope at home from a straw and a pin.

Teaching aids

An old torch, a 1.5 V cell, an LED, copper sulphate, a nail and a battery for an electromagnet; real samples of fuses and MCBs; flash cards of circuit symbols.

Common misconceptions

'A cell has electricity stored in it that gets used up in the bulb' (in reality, charge circulates in the circuit while energy is converted); 'a single wire is enough to light a bulb' (a closed circuit is essential); 'current stops during a short circuit' (the opposite — it rises sharply); 'water always conducts' (distilled water is a weak conductor).

Assessment and safety

Show children an incomplete circuit diagram and ask why the bulb won't light. Emphasise safety: experiments should only use cells/batteries, never a home's mains socket.

Memory trick / exam tip

For static electricity: 'glass-silk = glass positive (+), straw-polythene = straw negative (-)' — just remember that silk 'takes' electrons. And reason through every safety question using I = V/R: resistance dropped (short circuit) or total current increased (overloading) → heat increased → fuse melted.

REET 2024 questions (solved)

Question 121

At the time of short circuit, the current in the circuit

  1. Aपर्याप्त कमी होती है
  2. Bनिरंतर परिवर्तित होती है
  3. Cबहुत अधिक बढ़ जाती है
  4. Dपरिवर्तित नहीं होती है

Explanation

लघुपथन (short circuit) में जीवित (live) और उदासीन (neutral) तार सीधे संपर्क में आ जाते हैं, जिससे परिपथ का प्रतिरोध लगभग शून्य हो जाता है। ओम के नियम I = V/R के अनुसार प्रतिरोध बहुत कम होने से धारा बहुत अधिक बढ़ जाती है। इसी से अत्यधिक ऊष्मा बनती है और फ्यूज़ उड़ जाता है।

Question 144

When the glass rod is rubbed with the silk cloth, then glass rod will become

  1. Aविद्युत उदासीन
  2. Bधनावेशित
  3. Cऋणावेशित
  4. Dउपरोक्त में से कोई नहीं

Explanation

काँच की छड़ को रेशम से रगड़ने पर छड़ से कुछ इलेक्ट्रॉन रेशम में चले जाते हैं। इलेक्ट्रॉन खोने के कारण काँच की छड़ धनावेशित (positively charged) और इलेक्ट्रॉन पाने के कारण रेशम ऋणावेशित हो जाता है।

Question 143

Two statements are given below i. When a plastic straw is rubbed with polythene it becomes negatively charged. ii. When a glass rod is rubbed with silk, it becomes negatively charged. Then the false statements is/are

  1. Aकेवल (i)
  2. Bकेवल (ii)
  3. C(i) व (ii) दोनों
  4. Dउपरोक्त में से कोई नहीं

Explanation

प्लास्टिक स्ट्रॉ को पॉलिथीन से रगड़ने पर स्ट्रॉ ऋणावेशित हो जाती है, इसलिए कथन (i) सही है (NCERT कक्षा 8)। काँच की छड़ को रेशम से रगड़ने पर काँच की छड़ इलेक्ट्रॉन खोकर धनावेशित होती है, ऋणावेशित नहीं। अतः केवल कथन (ii) गलत है।

Practice questions

Question 1

How is an ammeter connected in a circuit to measure electric current?

  1. Aसमांतर क्रम में
  2. Bश्रेणी क्रम में
  3. Cभूसंपर्कित करके
  4. Dपरिपथ से अलग रखकर

Explanation

An ammeter is connected in series so that the entire current passes through it. A voltmeter is instead connected in parallel.

Question 2

A charge of 20 coulombs flows through a conductor in 10 seconds. The current is —

  1. A200 A
  2. B0.5 A
  3. C2 A
  4. D30 A

Explanation

I = Q/t = 20 C / 10 s = 2 A.

Question 3

Two resistors of 3 Ω and 6 Ω are connected in parallel. The equivalent resistance is —

  1. A9 Ω
  2. B2 Ω
  3. C4.5 Ω
  4. D18 Ω

Explanation

1/R = 1/3 + 1/6 = 2/6 + 1/6 = 3/6 = 1/2, so R = 2 Ω. In a parallel arrangement, the equivalent resistance is always smaller than even the smallest individual resistance.

Question 4

Which material's wire is generally used in the heating element of an electric heater?

  1. Aताँबा
  2. Bनाइक्रोम
  3. Cएल्युमिनियम
  4. Dचाँदी

Explanation

Nichrome has high resistance and doesn't oxidise quickly even at high temperatures, which is why it is used in heating elements. Copper and aluminium, having low resistance, are used in connecting wires instead.

Question 5

In electroplating with copper sulphate solution, copper gets deposited on which electrode?

  1. Aबैटरी के धन टर्मिनल से जुड़े इलेक्ट्रोड पर
  2. Bबैटरी के ऋण टर्मिनल से जुड़े इलेक्ट्रोड पर
  3. Cदोनों इलेक्ट्रोड पर बराबर
  4. Dकिसी पर नहीं, केवल गैस बनती है

Explanation

Copper deposits at the electrode connected to the battery's negative terminal, while copper dissolves into the solution from the plate connected to the positive terminal. This is why the object to be plated is connected to the negative terminal.

Question 6

In a tester for weakly conducting solutions, an LED is used instead of a bulb because —

  1. ALED अधिक ऊष्मा देती है
  2. BLED बहुत कम धारा पर भी चमकती है
  3. CLED को सेल की आवश्यकता नहीं होती
  4. DLED धारा को बढ़ा देती है

Explanation

A weak conducting solution allows only a very small current to flow, which isn't enough to heat a bulb's filament and make it glow; an LED lights up even at this very low current.

Question 7

Who discovered that a magnetic needle is deflected near a current-carrying wire?

  1. Aमाइकल फ़ैराडे
  2. Bहैंस क्रिश्चियन ओर्स्टेड
  3. Cजॉर्ज साइमन ओम
  4. Dएलेसेंड्रो वोल्टा

Explanation

Oersted observed that a compass needle placed near a current-carrying wire gets deflected — this was the discovery of the magnetic effect of current.

Question 8

One 'unit' of energy in an electricity bill equals —

  1. A1 वाट-सेकंड
  2. B1 किलोवाट-घंटा = 3.6 × 10⁶ J
  3. C1 जूल
  4. D1000 जूल

Explanation

1 kWh = 1000 W × 3600 s = 3.6 × 10^6 J; this is exactly one 'unit' on a household electricity bill.

Question 9

A Class 6 student believes that 'a bulb will glow if only one wire connects it to a cell.' The most effective way to change this idea is —

  1. Aउसे सही उत्तर लिखकर याद करने को कहना
  2. Bविद्यार्थी से स्वयं एक तार और फिर दो तार से परिपथ बनवाकर परिणाम की तुलना कराना
  3. Cग़लती पर अंक काट लेना
  4. Dअगले पाठ पर आगे बढ़ जाना

Explanation

Building the circuit themselves — first with one wire, then with two — and comparing the outcome, when the bulb doesn't light with just one wire, creates a cognitive conflict in the child's mind, and they build the concept of a closed circuit for themselves — this is the constructivist approach.

Question 10

Which is the safest behaviour during lightning in a thunderstorm?

  1. Aखुले मैदान में किसी अकेले ऊँचे पेड़ के नीचे खड़े होना
  2. Bछाता ऊपर उठाकर खुले में चलना
  3. Cकिसी घर या बंद इमारत के अंदर रहना
  4. Dपानी के तालाब में तैरना

Explanation

A house or an enclosed building is the safest place. Standing alone under a tall tree in an open field, holding up a metal umbrella in the open, and being in water are all dangerous during lightning (NCERT Class 8).

Frequently asked questions

What is the SI unit of electric current?+

The ampere (A). 1 ampere is the flow of 1 coulomb of charge per second. Current is measured with an ammeter.

What happens to the current in a short circuit?+

In a short circuit, resistance drops to nearly zero, so according to I = V/R the current rises sharply, and the fuse wire melts.

What charge does rubbing a glass rod with silk produce?+

The glass rod loses electrons and becomes positively charged, while the silk gains electrons and becomes negatively charged.

What is a fuse wire made of?+

A fuse wire is made of a low-melting-point material, which heats up and melts when current beyond the safe limit flows through it, breaking the circuit.

How many questions come from Electric Current in REET?+

REET 2024 (Level 2 Science) carried 3 questions from this topic — 1 on short circuits and 2 on static electricity (charge from rubbing).

Read next

Sound

Previous topic: transmission of sound, frequency and audibility

Magnetism

Next topic: properties of magnets, poles and electromagnets

REET Syllabus

The complete official syllabus for Level 2 Maths-Science

REET 2024 Solved Paper

Questions, official answer key and explanations for all shifts

Official Sources

  1. NCERT Class 7 Science (Curiosity) — Chapter 3: Electricity: Circuits and their Components
  2. NCERT Science Class 10 — Electricity (Ohm's law, resistance, heating effect)
  3. BIPM — SI Brochure (definitions of ampere, coulomb, ohm)

Change Log

  • 17 September 2026 — English page published — mirrors the fact-checked Hindi page, independently bilingual-accuracy checked