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Basic Electricity

Basic Science & Engineering · Heat, Electricity & Technical Basics

Useful for: Railway RRB

Overview

Basic electricity covers current, voltage, resistance, Ohm’s law, AC/DC supply and measuring instruments.

Key points

Ohm’s law: V = IR.
Indian household supply: about 230 V AC at 50 Hz.
Ammeter is connected in series; voltmeter in parallel.
Series resistances add; parallel combination is smaller than the smallest resistance.
Conductors: copper, aluminium; insulators: rubber, PVC, mica.

Explanation

Resistance depends on length, area and material (resistivity).
DC flows in one direction; AC reverses periodically.
Transformers work only on AC.
Power P = VI.

Step by step

Identify the concept, tool or rule involved.
Recall the definition, value or procedure.
Check units, safety logic and the direction of the effect.

Examples

230 V across 46 Ω → I = 5 A.
Two 10 Ω resistors in series → 20 Ω.
Indian mains frequency → 50 Hz.

Traps and advanced points

Trap: Connecting an ammeter in parallel.
Trap: Thinking transformers work on DC.
Trap: Adding resistances in parallel.

Quick revision

V = IR.
Ammeter series, voltmeter parallel.
230 V, 50 Hz.

Practice MCQs

Static-GK drill: Malaria is caused by which type of organism?
1. Bacterium only
2. Plasmodium parasite
3. Fungus
4. Virus
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Answer: (b) Plasmodium parasite. Malaria is caused by Plasmodium parasite.
Static-GK drill: The functional unit of the kidney is what?
1. Villus
2. Nephron
3. Neuron
4. Alveolus
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Answer: (b) Nephron. The functional unit of the kidney is Nephron.
Static-GK drill: What is the SI unit of electric current?
1. volt
2. ampere
3. coulomb
4. ohm
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Answer: (b) ampere. Ampere is the SI unit of electric current.
Static-GK drill: Which component of blood is central to clotting?
1. Neurons
2. Platelets
3. Plasma water only
4. Red blood cells only
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Answer: (b) Platelets. Platelets is central to clotting.
Static-GK drill: Which organelle is the main site of protein synthesis?
1. Ribosome
2. Nucleus
3. Mitochondrion
4. Vacuole
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Answer: (a) Ribosome. Ribosome is the main site of protein synthesis.
ALP Basic Science & Engineering: Which statement opening is correctly completed by “1/R = 1/R₁ + 1/R₂”?
1. moment of a force is
2. mechanical advantage of a machine is
3. two resistors in parallel have equivalent resistance satisfying
4. RAM is primarily
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Answer: (c) two resistors in parallel have equivalent resistance satisfying. Parallel combination reduces equivalent resistance.
ALP Basic Science & Engineering: Complete the statement: “Two resistors in series have equivalent resistance ____.”
1. R₁ + R₂
2. volatile working memory
3. length plus unpredictable character combinations
4. small lengths/diameters with finer precision
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Answer: (a) R₁ + R₂. Series resistances add directly.
ALP Basic Science & Engineering: Complete the statement: “Two resistors in parallel have equivalent resistance satisfying ____.”
1. Central Processing Unit
2. R₁ + R₂
3. 1/R = 1/R₁ + 1/R₂
4. kilogram
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Answer: (c) 1/R = 1/R₁ + 1/R₂. Parallel combination reduces equivalent resistance.
ALP Basic Science & Engineering: Which statement opening is correctly completed by “R₁ + R₂”?
1. work is measured in
2. two resistors in series have equivalent resistance
3. earthing primarily provides
4. greenhouse effect is intensified by increased atmospheric
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Answer: (b) two resistors in series have equivalent resistance. Series resistances add directly.
ALP Basic Science & Engineering: Which statement opening is correctly completed by “P = VI”?
1. first aid for severe electrical shock begins with
2. electrical power in a DC circuit can be written as
3. two resistors in series have equivalent resistance
4. power is measured in
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Answer: (b) electrical power in a DC circuit can be written as. Also P = I²R or V²/R when Ohm’s law applies.