ELECTRICITY

Introduction

Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. It is the fundamental energy source of the modern world, powering everything from lightbulbs to supercomputers.

Brief Overview

mindmap root((Electricity)) Charge Positive Negative Current Flow of Electrons Voltage Electrical Pressure Resistance Opposition to Flow

1. Electric Charge and Current

Electric Charge ($q$): A fundamental property of matter. Protons have a positive charge (+), electrons have a negative charge (-). Like charges repel; opposite charges attract. The unit of charge is the Coulomb (C).
Electric Current ($I$): The rate of flow of electric charge (specifically, the flow of electrons through a conductor).
- Unit: Ampere (A). 1 Ampere means 1 Coulomb of charge is flowing past a point every second.
- Formula: $I = \frac{q}{t}$ (Current = Charge / Time).
Direction of Current: By historical convention, we say "conventional current" flows from Positive to Negative. However, we now know that actual electrons flow from Negative to Positive.

MCQs - Charge and Current

The fundamental unit of electric charge is the:
a) Volt
b) Ampere
c) Coulomb
d) Ohm
Answer: c
Electric current is defined as the rate of flow of:
a) Protons
b) Neutrons
c) Electric charge (electrons)
d) Atoms
Answer: c
Which of the following statements is true regarding electric charges?
a) Like charges attract, opposite charges repel
b) Like charges repel, opposite charges attract
c) Both positive and negative charges repel each other
d) Charges have no effect on each other
Answer: b
What is the standard unit of measurement for electric current?
a) Watt
b) Volt
c) Joule
d) Ampere
Answer: d
Conventional electric current is said to flow from:
a) Positive to Negative
b) Negative to Positive
c) North to South
d) South to North
Answer: a
If an object gains electrons, what is its overall charge?
a) Positive
b) Negative
c) Neutral
d) Alternating
Answer: b
What is the standard symbol used to denote electric charge?
a) C
b) I
c) q
d) E
Answer: c
Which of the following is true about protons?
a) They carry a negative charge
b) They carry a positive charge
c) They are neutrally charged
d) They orbit the nucleus
Answer: b
Current can only flow if there is a:
a) Complete and closed path
b) Broken wire
c) Source of sound
d) Vacuum
Answer: a
The formula $I = q / t$ implies that time ($t$) must be measured in:
a) Hours
b) Minutes
c) Seconds
d) Milliseconds
Answer: c

2. Voltage, Resistance, and Ohm's Law

Voltage / Potential Difference ($V$): The "push" or electrical pressure that causes electrons to flow through a circuit. It is the work done to move a unit charge from one point to another.
- Unit: Volt (V).
Resistance ($R$): The opposition a material offers to the flow of electric current. It acts like friction in a pipe.
- Unit: Ohm ($\Omega$).
Ohm's Law: The most important law in basic circuits. It states that the current flowing through a conductor is directly proportional to the voltage applied across it, provided the temperature remains constant.
- Formula: $V = I \times R$ (Voltage = Current $\times$ Resistance).

MCQs - Ohm's Law

The "electrical pressure" that causes current to flow is called:
a) Resistance
b) Voltage
c) Amperage
d) Wattage
Answer: b
The opposition to the flow of electric current is measured in:
a) Ohms
b) Volts
c) Amperes
d) Joules
Answer: a
According to Ohm's law, the mathematical relationship between Voltage ($V$), Current ($I$), and Resistance ($R$) is:
a) $V = I / R$
b) $R = V \times I$
c) $V = I \times R$
d) $I = V \times R$
Answer: c
If a circuit has a resistance of 10 Ohms and a current of 2 Amperes, what is the voltage?
a) 5 Volts
b) 8 Volts
c) 12 Volts
d) 20 Volts
Answer: d ($V = 2 \times 10 = 20$)
If you increase the resistance in a circuit while keeping the voltage the same, the current will:
a) Increase
b) Decrease
c) Stay exactly the same
d) Stop completely
Answer: b
Ohm's law only holds true if which physical property remains constant?
a) Pressure
b) Volume
c) Mass
d) Temperature
Answer: d
If the voltage across a resistor is doubled and the resistance remains the same, the current will:
a) Halve
b) Double
c) Quadruple
d) Stay the same
Answer: b
A circuit has a 12V battery and a 3 Ohm resistor. What is the current flowing?
a) 36 A
b) 9 A
c) 4 A
d) 15 A
Answer: c
Which device is typically used to measure resistance in a circuit?
a) Ammeter
b) Voltmeter
c) Ohmmeter
d) Galvanometer
Answer: c
If the current is 5A and resistance is 4 Ohms, what is the voltage drop?
a) 20 V
b) 9 V
c) 1.25 V
d) 0.8 V
Answer: a

3. Power and Circuits

Electric Power ($P$): The rate at which electrical energy is consumed or generated.
- Unit: Watt (W).
- Formula: $P = V \times I$ (Power = Voltage $\times$ Current). (Also $P = I^2R$ and $P = V^2/R$).
Series Circuit: Components are connected end-to-end in a single path. If one component breaks, the whole circuit stops working. The current is the same everywhere.
Parallel Circuit: Components are connected in multiple branches. If one branch breaks, the others keep working. The voltage is the same across all branches. This is how homes are wired!

MCQs - Power and Circuits

The rate at which electrical energy is consumed is called Electric Power, measured in:
a) Joules
b) Volts
c) Watts
d) Ohms
Answer: c
What is the formula for calculating electrical power if you know voltage and current?
a) $P = V / I$
b) $P = V \times I$
c) $P = I / V$
d) $P = V + I$
Answer: b
In which type of circuit are components connected in a single, continuous loop?
a) Parallel circuit
b) Open circuit
c) Series circuit
d) Short circuit
Answer: c
Why are houses wired in parallel circuits rather than series circuits?
a) It saves wire
b) It increases the total voltage
c) So that if one lightbulb burns out, the others stay on
d) Because series circuits are illegal
Answer: c
In a series circuit, which property remains constant across every component?
a) Voltage
b) Resistance
c) Power
d) Current
Answer: d
In a parallel circuit, which property remains the same across all branches?
a) Voltage
b) Current
c) Resistance
d) Power
Answer: a
Which formula correctly relates Power ($P$), Current ($I$), and Resistance ($R$)?
a) $P = I^2R$
b) $P = V^2 / R$
c) Both a and b
d) Neither a nor b
Answer: c
If a 100W lightbulb is operated at 100V, what is the current drawn?
a) 1 A
b) 10 A
c) 100 A
d) 0.1 A
Answer: a
What happens to the total resistance when you add more resistors in series?
a) It decreases
b) It increases
c) It remains the same
d) It drops to zero
Answer: b
If one bulb blows in a parallel circuit containing three bulbs, what happens to the other two?
a) They turn off
b) They remain on
c) They blink rapidly
d) They explode
Answer: b

Fun Facts about Electricity!

Speed of Electricity: While the electric signal (the electromagnetic wave) travels through a wire at nearly the speed of light (300,000 km/s), the actual individual electrons move incredibly slowly! This "drift velocity" is usually less than a millimeter per second.
Lightning: A single bolt of lightning can carry up to one billion volts of electricity and heat the surrounding air to $30,000^\circ C$ (five times hotter than the surface of the sun)!
Bioelectricity: Your body runs on electricity! Every time your heart beats, an electrical signal travels through the heart muscle to trigger the contraction. This is what an EKG (Electrocardiogram) measures.