Effects of Current: Electricity and Magnetic Effects
Effects of Current covers electricity and magnetic effects, combining circuit numericals with direction rules and device principles.
Electric current and circuits
Current I = Q/t, measured in amperes; potential difference V = W/Q, in volts. Ohm's law V = IR holds for metallic conductors at constant temperature. Resistance R = ρl/A: longer or thinner wires have more resistance. In series, current is the same and resistances add; in parallel, voltage is the same and 1/R = 1/R₁ + 1/R₂ + ... . Electrical power P = VI = I²R = V²/R; energy consumed = power × time. A fuse is a thin wire that melts on excess current; earthing gives a low-resistance path.
Magnetic effects
A current-carrying conductor produces a magnetic field; the right-hand thumb rule gives its direction. A solenoid behaves like a bar magnet. A force F = BIL sin θ acts on a current-carrying conductor in a magnetic field; Fleming's left-hand rule gives its direction, the principle of the electric motor. Electromagnetic induction produces a current when magnetic flux changes; Fleming's right-hand rule gives the direction, the principle of the generator. In India, domestic AC supply is 50 Hz, 220 V.
Worked example
A 6 Ω and a 3 Ω resistor are connected in parallel across a 6 V battery. Equivalent resistance: 1/R = 1/6 + 1/3 = 1/2, so R = 2 Ω. Total current I = V/R = 6/2 = 3 A. Branch currents: 6/6 = 1 A and 6/3 = 2 A, which add to 3 A. Total power P = VI = 6 × 3 = 18 W. The reasoning checks that parallel branches share voltage, not current.
Traps
An ammeter is connected in series and a voltmeter in parallel; reversed connections can damage them. Ohm's law is not universal for every device. In parallel, total resistance is less than the smallest resistance. Magnetic field directions are easily reversed; apply the rule carefully. Do not confuse the motor effect with electromagnetic induction.