Electricity and Magnetism forms a crucial chapter in the Bihar TET Paper II Science section, typically contributing 2-4 questions. This topic bridges abstract physics concepts with everyday applications that students encounter—from switching on lights to understanding how motors work. Mastery here demonstrates your ability to explain phenomena that children find fascinating yet often misunderstand.
For the exam, you must know the fundamentals of electric current, circuit components, Ohm's law, and how electricity and magnetism are interconnected. Questions often test conceptual clarity rather than complex calculations—understanding why a bulb glows, what happens when circuit elements are rearranged, or how an electromagnet differs from a permanent magnet. Bihar TET emphasizes practical applications relevant to upper-primary classrooms.
Key Concepts
**Electric current** is the flow of electric charges (electrons) through a conductor, measured in amperes (A). Current flows from positive to negative terminal in conventional terms, but electrons actually move in the opposite direction.
**Electric circuit** is a closed path through which current flows. It requires a source (cell/battery), conducting wires, a load (bulb/resistor), and optionally a switch. If the path breaks anywhere, current stops—this is an open circuit.
**Potential difference (voltage)** is the "push" that drives current through a circuit, measured in volts (V). Think of it as electrical pressure—without it, electrons won't move.
**Resistance** opposes the flow of current, measured in ohms (Ω). Materials like nichrome have high resistance (used in heaters), while copper has low resistance (used in wires).
**Series and parallel circuits** differ fundamentally: in series, current has only one path and remains same throughout; in parallel, current splits across multiple paths, and voltage remains same across each branch.
**Magnetic effect of current** states that every current-carrying conductor produces a magnetic field around it. This is the principle behind electromagnets, motors, and generators.
**Electromagnet** is a temporary magnet created by coiling wire around an iron core and passing current through it. Strength increases with more turns of wire and stronger current.
Formulas / Key Facts
**Ohm's Law:** V = I × R (Voltage equals Current multiplied by Resistance)
**Resistance in Series:** R_total = R₁ + R₂ + R₃ + ... (Resistances add up directly)
**Example 3: Electric Energy Calculation** A 100W bulb is used for 5 hours daily for 30 days. Calculate energy consumed in kWh.
Solution: Power = 100W = 0.1 kW Time = 5 × 30 = 150 hours Energy = P × t = 0.1 × 150 = 15 kWh
Energy consumed is 15 units.
Common Mistakes
**Confusing series and parallel properties** → In series, current is same everywhere but voltage divides; in parallel, voltage is same across branches but current divides. Remember: "Series = Same current, Parallel = Same potential."
**Mixing up conventional current and electron flow** → Conventional current flows positive to negative, but electrons actually flow negative to positive. Exam questions typically use conventional current direction.
**Believing thicker wires have more resistance** → Wrong. Thicker wires have less resistance because they offer more space for electron flow. Resistance is inversely proportional to cross-sectional area.
**Thinking electromagnets are permanent** → Electromagnets work only when current flows. Switch off current, magnetism disappears. This distinguishes them from permanent magnets.
**Forgetting to convert units** → Power is often given in watts but energy calculations need kilowatts for kWh. Always check: 1000W = 1kW before calculating electricity bills.
Quick Reference
Ohm's Law: V = IR (Voltage = Current × Resistance)
Series circuit: Same current, resistances add, voltage divides
Parallel circuit: Same voltage, currents add, equivalent resistance decreases
Fuse protects by melting when excess current flows
Electromagnet strength depends on current and number of coil turns
Right-hand thumb rule gives magnetic field direction around a current-carrying wire
You read the notes — now try one
A student connects a bulb, a cell, and a switch in a circuit. When the switch is open, the bulb does not glow. What is the reason for this?
Tap an option to check your answer.
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Invite your prep group — read the same notes, then discuss doubts in this topic's shared room.
A student connects a bulb, a cell, and a switch in a circuit. When the switch is open, the bulb does not glow. What is the reason for this?
Q2 · Electricity and Magnetism · MEDIUM
A copper wire carries an electric current from south to north. According to the right-hand thumb rule, if the thumb points in the direction of current, the fingers curl in the direction of the magnetic field. In which direction will the magnetic field lines circle around this wire at a point to the east of the wire?
Q3 · Electricity and Magnetism · MEDIUM
Three resistors of resistances 2 ohm, 3 ohm, and 6 ohm are connected in parallel across a 6 V battery. What is the total current supplied by the battery? (Assume the battery has negligible internal resistance.)
Q4 · Electricity and Magnetism · HARD
A rectangular coil of 50 turns, each of area 0.1 square metre, is suspended in a uniform magnetic field of 0.02 T. The plane of the coil is initially parallel to the magnetic field. The coil is rotated through 90 degrees so that its plane becomes perpendicular to the field. If this rotation takes 0.05 seconds, what is the magnitude of the average induced emf in the coil?
Q5 · Electricity and Magnetism · MEDIUM
In an electric circuit, the device used to measure electric current is called: