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Electricity & Magnetism

General Science · Physics

Useful for: Railway RRB, CTET, OTET, OSSTET, OSSC RHT — Regular High School Teacher, CSIR NET, CTSA / STSS, Junior Teacher

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Overview

Electric current flows through circuits according to Ohm’s law; currents produce magnetic effects used in motors and generators.

Key points

Ohm’s law: V = IR.
Series: R = R₁ + R₂; parallel: 1/R = 1/R₁ + 1/R₂.
Power P = VI = I²R = V²/R.
1 unit of electricity = 1 kWh.
Electric motors use Fleming’s left-hand rule; generators use the right-hand rule.

Explanation

Household wiring is in parallel so each appliance gets full voltage.
A fuse melts when current is too high.
Earthing protects against shocks.
An electromagnet becomes a magnet only when current flows.

Step by step

Identify the concept or law involved.
Recall the definition, unit or formula.
Check units and the direction of the effect before choosing.

Examples

6 Ω and 3 Ω in parallel: R = 18/9 = 2 Ω.
220 V × 5 A = 1,100 W.
A 100 W bulb used for 10 h consumes 1 kWh (1 unit).

Traps and advanced points

Trap: Adding resistances in parallel.
Trap: Thinking household wiring is series.
Trap: Mixing left- and right-hand rules.

Quick revision

V = IR.
P = VI.
1 unit = 1 kWh.

Practice MCQs

Cholera is caused by which bacterium?
1. Salmonella typhi
2. Vibrio cholerae
3. Mycobacterium tuberculosis
4. HIV
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Answer: (b) Vibrio cholerae. Cholera is caused by Vibrio cholerae.
Lemon juice is rich in which acid?
1. Hydrochloric acid
2. Oxalic acid only
3. Acetic acid
4. Citric acid
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Answer: (d) Citric acid. Lemon juice is rich in Citric acid.
The SI unit of power is what?
1. newton
2. watt
3. joule
4. pascal
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Answer: (b) watt. The SI unit of power is watt.
Vitamin D deficiency in children can cause what?
1. Beriberi
2. Rickets
3. Scurvy
4. Pellagra
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Answer: (b) Rickets. Vitamin D deficiency in children can cause Rickets.
Which bone is the longest in the human body?
1. Tibia
2. Femur
3. Radius
4. Humerus
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Answer: (b) Femur. Femur is the longest in the human body.
Which option correctly answers this General Science check: SI unit of force?
1. newton
2. NaCl
3. 3 × 10^8 m/s
4. radiation
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Answer: (a) newton. F = ma; 1 newton = 1 kg·m/s².
Which option correctly answers this General Science check: heat transfer through vacuum mainly occurs by?
1. acidic solution
2. 9.8 m/s²
3. radiation
4. moisture
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Answer: (c) radiation. Conduction/convection require material medium; radiation does not.
Which option correctly answers this General Science check: frequency is measured in?
1. mitochondria
2. hertz
3. rate of reaction
4. convex mirror
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Answer: (b) hertz. 1 hertz means one cycle per second.
Which of these is a good conductor of electricity?
1. rubber
2. wood
3. copper
4. plastic
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Answer: (c) copper. Metals such as copper conduct electricity.
Ohm’s law states that V equals —
1. R/I
2. I²R
3. I/R
4. IR
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Answer: (d) IR. V = IR at constant temperature.