Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Electric charge is measured in Coulombs (). There are two types: positive and negative. Like charges repel, and opposite charges attract.
Electric current () is the rate of flow of charge. It is measured in Amperes ().
Conventional current flows from the positive terminal to the negative terminal, while electrons flow from negative to positive.
Electromotive force (e.m.f.) and Potential Difference (p.d.) are measured in Volts (). One Volt is defined as .
Resistance () is the property of a conductor to oppose the flow of current, measured in Ohms (). For an Ohmic conductor, .
In a series circuit, the current is the same at all points, while the total p.d. is the sum of p.d. across individual components.
In a parallel circuit, the p.d. across each branch is the same, and the total current is the sum of the currents in the individual branches.
Magnetic field lines always point from the North pole to the South pole. The density of lines represents the strength of the field.
Fleming's Left-Hand Rule is used to determine the direction of the force on a current-carrying conductor in a magnetic field (Thumb: Motion, First finger: Field, Second finger: Current).
Faraday's Law of Electromagnetic Induction states that the induced e.m.f. is proportional to the rate of change of magnetic flux linkage.
Lenz's Law states that the direction of an induced current is such that it opposes the change that produced it.
Transformers change the voltage of an alternating current () using two coils. A step-up transformer increases voltage, while a step-down transformer decreases it.
📐Formulae
I_p V_p = I_s V_s \text{ (for 100% efficiency)}
💡Examples
Problem 1:
A circuit contains two resistors connected in parallel with resistances and . A battery is connected across the combination. Calculate the total resistance of the circuit and the total current flowing from the battery.
Solution:
First, calculate total resistance () for parallel: . Thus, . Next, use Ohm's Law for total current: .
Explanation:
In a parallel circuit, the reciprocal of the total resistance is the sum of the reciprocals of individual resistances. Once is found, the total current is determined by dividing the supply voltage by .
Problem 2:
A transformer has turns on the primary coil and turns on the secondary coil. If the input voltage is , calculate the output voltage.
Solution:
Using the transformer equation: . Rearranging for : .
Explanation:
This is a step-up transformer because the number of turns on the secondary coil () is greater than the number of turns on the primary coil (). The output voltage increases by the same factor as the turns ratio.