Electricity, Ohm's Law, and Resistance Flashcards

Flashcards testing core concepts, definitions, formulas, and relationships regarding electrical current, potential difference, Ohm's law, resistance, and specific resistance based on the provided lecture transcript.

How is a voltmeter connected in an electric circuit to measure potential difference?

It is connected across the points in parallel with the circuit, taking care that its positive (+ve) marked terminal is connected to the higher potential point.

How is $1\,\text{volt}$ defined in terms of work done and electric charge?

The potential difference between two points is said to be $1\,\text{volt}$ if the work done in moving $1\,\text{coulomb}$ charge from one point to the other is $1\,\text{joule}$ ($1\,\text{volt} = \frac{1\,\text{joule}}{1\,\text{coulomb}}$).

What happens to electrons when a potential difference is applied across the ends of a metallic wire?

The electrons experience a force towards the positive potential end and begin to drift towards it, continuously colliding with fixed positive ions and losing kinetic energy which heats up the wire.

What is the definition of electrical resistance?

Resistance is the obstruction offered to the flow of current by the conductor (or wire).

What is the primary cause of electrical resistance in a metal conductor?

The collisions suffered by moving free electrons with fixed positive ions inside the conductor while moving from one end to the other end.

What is the statement of Ohm's law established by Georg Simon Ohm in 1826?

The current flowing in a conductor is directly proportional to the potential difference applied across its ends, provided that the physical conditions and the temperature of the conductor remain constant ($I \propto V$).

What is the mathematical equation for Ohm's law, and what is $R$?

$V = IR$, where $V$ is potential difference, $I$ is current, and $R$ is a constant at a given temperature called the resistance of the conductor.

How is $1\,\text{ohm}$ of resistance defined?

The resistance of a conductor is said to be $1\,\text{ohm}$ if $1\,\text{ampere}$ current flows through it when a potential difference of $1\,\text{volt}$ is applied across the ends of the conductor ($1\,\text{ohm} = \frac{1\,\text{volt}}{1\,\text{ampere}}$).

What are the values of $1\,\text{kilo-ohm}$ ($1\,\text{k}\Omega$) and $1\,\text{mega-ohm}$ ($1\,\text{M}\Omega$) in ohms?

$1\,\text{kilo-ohm} = 10^3\,\Omega$ and $1\,\text{mega-ohm} = 10^6\,\Omega$.

What is conductance, and what are its units?

Conductance ($G$) is the reciprocal of resistance ($\text{Conductance} = \frac{1}{\text{Resistance}}$). Its unit is ohm$^{-1}$($\Omega^{-1}$) or siemen (symbol$\text{S}$$).

What physical quantity does the slope of an $I\text{-}V$ graph represent?

The slope of an $I\text{-}V$ graph represents $\frac{\Delta I}{\Delta V}$, which is the reciprocal of the resistance of the conductor ($\text{Slope} = \frac{1}{R}$).

What physical quantity does the slope of a $V\text{-}I$ graph represent?

The slope of a $V\text{-}I$ graph represents $\frac{\Delta V}{\Delta I}$, which gives the resistance ($R$) of the conductor.

In the experimental verification of Ohm's law, which components are connected in series with the battery?

The rheostat ($Rh$), ammeter ($A$), resistance wire ($R$), and key ($K$) are connected in series with the battery ($B$).

What are ohmic resistors, and what are examples of them?

Ohmic resistors (linear resistances) are conductors that obey Ohm's law, where $\frac{V}{I}$ is constant. Examples include metallic conductors (silver, aluminium, copper, iron), nichrome, copper sulphate solution with copper electrodes, and dilute sulphuric acid at a constant temperature.

What are non-ohmic resistors, and what are examples of them?

Non-ohmic resistors (non-linear resistances) are conductors that do not obey Ohm's law. Examples include LEDs, solar cells, junction diodes, transistors, and the filament of a bulb.

What is dynamic resistance in a non-ohmic conductor?

Dynamic resistance is the value $\frac{\Delta V}{\Delta I}$ obtained by finding the slope of the tangent drawn at a corresponding point on the $V\text{-}I$ graph, which is different for different values of $V$ or $I$.

What four factors affect the resistance of a conductor?

(1) Material of conductor, (2) length of conductor, (3) thickness of conductor, and (4) temperature of conductor.

How does resistance depend on the length and cross-sectional area of a wire?

Resistance is directly proportional to length ($R \propto l$) and inversely proportional to the area of cross section ($R \propto \frac{1}{a}$ or $R \propto \frac{1}{r^2}$).

Why does the resistance of a conductor increase with an increase in temperature?

With an increase in temperature, the random motion of free electrons increases, resulting in a higher number of collisions of electrons with fixed positive ions.

On a $V\text{-}I$ graph for a conductor at temperatures $T_1$ and $T_2$ where $T_1 > T_2$, which line is steeper and why?

The straight line for $T_1$ is steeper because the resistance of the conductor is greater at high temperature $T_1$ than at low temperature $T_2$.

What is the formula and definition for specific resistance (resistivity) $\rho$?

$\rho = \frac{R a}{l}$. Specific resistance is the resistance of a wire of that material of unit length and unit area of cross section (or the resistance between opposite faces of a unit cube).

What is the S.I. unit of specific resistance (resistivity)?

The S.I. unit of specific resistance is $\text{ohm} \times \text{metre}$ (or $\Omega \cdot \text{m}$).