Quick Review Flashcards - Click to flip and test your knowledge!
Question
What is the physical process by which a glass rod becomes positively charged when rubbed with silk?
Answer
The glass rod loses electrons to the silk.
Question
According to the principle of quantization, what is the formula for the total charge $q$ on a body?
Answer
$q = \pm ne$ (where $n$ is an integer and $e$ is the elementary charge).
Question
What is the S.I. unit of electric charge?
Answer
The coulomb (symbol $C$).
Question
How many electrons are required to constitute a total charge of $1$ $C$?
Answer
$6.25 \times 10^{18}$ electrons.
Question
Why is the charge in a non-conductor (insulator) described as 'static'?
Answer
The charge resides at a fixed point and does not flow.
Question
What defines the 'current' flowing in a conductor?
Answer
The rate of flow of charge across any cross-section.
Question
Concept: $1$ Ampere
Answer
Definition: The current that flows when one coulomb of charge passes through a conductor cross-section in one second.
Question
Current is measured using a/an _____ connected in series with the circuit.
Answer
ammeter
Question
In a metallic conductor, which particles are responsible for the flow of current?
Answer
Free electrons.
Question
In an electrolyte, the current is constituted by the movement of both _____ and _____.
Answer
cations (positive ions); anions (negative ions)
Question
How is the direction of conventional current defined relative to the motion of electrons?
Answer
The direction of current is opposite to the direction of motion of electrons.
Question
Define 'electric potential' at a point.
Answer
The work done per unit charge in bringing a positive test charge from infinity to that point.
Question
What is the mathematical relation between potential ($V$), work ($W$), and charge ($Q$)?
Answer
$V = \frac{W}{Q}$
Question
What is the S.I. unit of potential difference?
Answer
The volt ($V$).
Question
Term: Potential Difference (p.d.)
Answer
Definition: The work done per unit charge in moving a positive test charge from one point to another.
Question
A voltmeter used to measure potential difference must be connected in _____ with the circuit component.
Answer
parallel
Question
What is the primary cause of electrical resistance in a metallic conductor?
Answer
Collisions of free electrons with the fixed positive ions of the conductor.
Question
State Ohm's Law.
Answer
Current flowing in a conductor is directly proportional to the potential difference across its ends, provided temperature and physical conditions remain constant.
Question
What does the slope of a potential difference ($V$) versus current ($I$) graph represent for a conductor?
Answer
The resistance ($R$) of the conductor.
Question
What does the slope of a current ($I$) versus potential difference ($V$) graph represent?
Answer
The conductance (or the reciprocal of resistance) of the conductor.
Question
Define an 'Ohmic resistor'.
Answer
A conductor that obeys Ohm's Law, resulting in a linear $V-I$ graph passing through the origin.
Question
How does the $V-I$ graph of a non-ohmic resistor differ from that of an ohmic resistor?
Answer
The $V-I$ graph is a curve rather than a straight line.
Question
Term: Conductance
Answer
Definition: The reciprocal of resistance ($G = \frac{1}{R}$), measured in units of $ohm^{-1}$ ($\Omega^{-1}$) or siemen ($S$).
Question
What are the four factors that affect the resistance of a conductor?
Answer
Material, length, thickness (area of cross-section), and temperature.
Question
How does the resistance of a wire change if its length is doubled?
Answer
The resistance is doubled ($R \propto l$).
Question
How does the resistance of a conductor vary with its area of cross-section ($a$)?
Answer
Resistance is inversely proportional to the area of cross-section ($R \propto \frac{1}{a}$).
Question
Why does the resistance of a metallic conductor increase with an increase in temperature?
Answer
Increased temperature increases the random motion of electrons, leading to more frequent collisions with positive ions.
Question
Concept: Specific Resistance (Resistivity)
Answer
Definition: The resistance of a wire of that material with unit length and unit area of cross-section.
Question
What is the S.I. unit of specific resistance ($\rho$)?
Answer
The ohm-metre ($\Omega \cdot m$).
Question
How does resistivity (specific resistance) differ from resistance in terms of the conductor's dimensions?
Answer
Resistivity is a characteristic property of the material and is independent of the conductor's shape and size.
Question
For which class of materials does specific resistance decrease with an increase in temperature?
Answer
Semiconductors.
Question
Why are copper and aluminium preferred for electrical power transmission wires?
Answer
They have very low specific resistance, which minimises energy loss due to heating.
Question
Why is manganin or constantan used to make standard resistors?
Answer
They have high specific resistance that remains practically unchanged with variations in temperature.
Question
What are the two essential properties of a material used for a fuse wire?
Answer
Low melting point and high specific resistance.
Question
Define a 'superconductor'.
Answer
A substance that has zero resistance (infinite conductance) at a very low temperature.
Question
Define the 'electromotive force' (e.m.f.) of a cell.
Answer
The energy spent per unit charge in taking a positive test charge around the complete circuit (including inside the cell).
Question
Under what condition is the terminal voltage ($V$) of a cell equal to its e.m.f. ($\epsilon$)?
Answer
When no current is drawn from the cell (open circuit).
Question
Define 'terminal voltage' of a cell.
Answer
The work done per unit charge in carrying a positive test charge around the external circuit connected across the cell terminals.
Question
Concept: Voltage Drop ($v$)
Answer
Definition: The energy spent per unit charge in carrying a positive test charge through the electrolyte inside the cell.
Question
What is the formula relating e.m.f. ($\epsilon$), terminal voltage ($V$), and voltage drop ($v$)?
Answer
$\epsilon = V + v$
Question
Define 'internal resistance' ($r$) of a cell.
Answer
The resistance offered by the electrolyte inside the cell to the flow of current.
Question
How does increasing the distance between electrodes affect a cell's internal resistance?
Answer
It increases the internal resistance.
Question
What is the total resistance of a circuit containing an external resistor $R$ and a cell with internal resistance $r$?
Answer
$R + r$
Question
What is the formula for calculating internal resistance ($r$) using e.m.f. ($\epsilon$), terminal voltage ($V$), and external resistance ($R$)?
Answer
$r = (\frac{\epsilon}{V} - 1)R$
Question
In a series combination of resistors, what is the formula for the equivalent resistance $R_s$?
Answer
$R_s = R_1 + R_2 + ... + R_n$
Question
Which physical quantity remains the same across each resistor in a series combination?
Answer
Current ($I$).
Question
In a parallel combination of resistors, which physical quantity is identical for all resistors?
Answer
Potential difference ($V$).
Question
What is the formula for the equivalent resistance $R_p$ of resistors connected in parallel?
Answer
$\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + ... + \frac{1}{R_n}$
Question
How does the equivalent resistance of a parallel combination compare to the value of the smallest individual resistor in that combination?
Answer
The equivalent resistance is less than the smallest individual resistance.
Question
Formula: Electrical Energy ($W$)
Answer
$W = VIt = I^2Rt = \frac{V^2t}{R}$
Question
What is the S.I. unit of electrical energy?
Answer
The joule ($J$).
Question
Define 'electrical power'.
Answer
The rate at which electrical energy is supplied by a source (or consumed by an appliance).
Question
Formula: Electrical Power ($P$)
Answer
$P = VI = I^2R = \frac{V^2}{R}$
Question
What is the commercial unit of electrical energy?
Answer
The kilowatt-hour ($kWh$).
Question
How many Joules are equivalent to $1$ $kWh$?
Answer
$3.6 \times 10^6$ $J$.
Question
From the power rating ($P$) and voltage rating ($V$) of an appliance, how is its resistance ($R$) calculated?
Answer
$R = \frac{V^2}{P}$
Question
What does the 'safe current' limit for an appliance mean?
Answer
The maximum current that can flow through the appliance without damaging its element or blowing its fuse.
Question
According to Joule's law of heating, the amount of heat produced ($H$) is directly proportional to the _____ of the current.
Answer
square ($I^2$)
Question
What are the three factors on which the heat produced in a wire depends?
Answer
Current ($I$), resistance ($R$), and time ($t$).
Question
How is the household consumption of electrical energy (in $kWh$) calculated for an appliance?
Answer
Energy ($kWh$) = $\frac{P(watt) \times t(hour)}{1000}$