Electricity - Comprehensive Practice Flashcards

Flashcards covering key definitions, equations, laws, circuit components, combination systems, heating effects, electric power, and practical activities from the Electricity lecture notes.

What is electric current, and what carries it through a conductor?

Electric current is the flow of electric charge through a conductor, typically carried by moving electrons. It represents the amount of charge flowing through a particular area in unit time.

What is the mathematical equation for electric current $I$ in terms of charge $Q$ and time $t$?

$$I = \frac{Q}{t}$$

What are the SI units of electric current and electric charge?

The SI unit of electric current is the ampere ($\text{A}$), and the SI unit of electric charge is the coulomb ($\text{C}$).

How is the direction of electric current defined in a circuit relative to electron flow?

Current flows from the positive terminal to the negative terminal of a cell or battery, which is opposite to the direction of electron flow.

What instrument is used to measure electric current, and how must it be connected in a circuit?

An ammeter is used to measure electric current, and it is always connected in series.

What is electric potential?

Electric potential is the amount of work done in bringing a unit positive charge from infinity to a point in an electric field, measured in volts ($\text{V}$).

How is potential difference ($V$) defined, and what is its formula in terms of work done ($W$) and charge ($Q$)?

Potential difference (voltage) is the difference in electric potential between two points in a circuit responsible for driving current flow. Its formula is $V = \frac{W}{Q}$.

How is one volt ($1\,\text{V}$) defined?

One volt is the potential difference between two points when $1\,\text{J}$ of work is done to move a charge of $1\,\text{C}$ from one point to the other ($1\,\text{V} = \frac{1\,\text{J}}{1\,\text{C}}$).

What device is used to measure electric potential difference, and how is it connected?

A voltmeter is used to measure potential difference, and it is always connected in parallel.

What law is illustrated by this straight-line graph of potential difference versus current?

It illustrates Ohm's law, which shows that as current through a conductor increases, the potential difference across it increases proportionally.

What does Ohm's Law state?

Ohm's Law states that the potential difference ($V$) across a wire in a circuit is directly proportional to the current ($I$) flowing through it, provided the temperature remains constant ($V \propto I$ or $V = I R$).

What is electrical resistance, and what is its SI unit?

Resistance ($R$) is a property of a conductor that inhibits charge flow. Its SI unit is the ohm ($\Omega$), where $1\,\Omega = \frac{1\,\text{V}}{1\,\text{A}}$.

How does current change when the resistance of a component is doubled at a constant voltage?

Current is inversely proportional to resistance, so doubling the resistance halves the current.

What is the function of a rheostat in an electric circuit?

A rheostat (variable resistance) is used to adjust the electric current in a circuit without altering the voltage source.

What three factors determine the resistance of a conductor?

1. Its length ($l$)
2. Its area of cross-section ($A$)
3. The nature of its material.

What is the formula for resistance ($R$) in terms of resistivity ($\rho$), length ($l$), and area ($A$)?

$$R = \rho \frac{l}{A}$$

What is electrical resistivity ($\rho$), and what is its SI unit?

Electrical resistivity is a measure of opposition to the flow of electric current characteristic of a material; its SI unit is the ohm meter ($\Omega\,\text{m}$).

Why are alloys commonly preferred over pure metals in electrical heating devices?

Alloys have higher resistivity than individual metals and resist oxidation (burning) at high temperatures.

Which metal is used for electric bulb filaments, and which metals are used for electrical transmission lines?

Tungsten is preferred for electric bulb filaments due to its high melting point, while copper and aluminum are commonly used for electrical transmission lines.

In a series combination of resistors, how do current and voltage behave across each component?

Current remains constant throughout the circuit and each resistor, while potential difference varies across each resistor.

What is the formula for the total equivalent resistance ($R_s$) of three resistors in series?

$$R_s = R_1 + R_2 + R_3$$

In a parallel combination of resistors, how do voltage and current behave across each component?

Voltage remains constant across each resistor, while electric current varies across each parallel branch.

What is the formula for the total equivalent resistance ($R_p$) of three resistors in parallel?

\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}

Why is a series connection impractical for connecting an electric bulb and a heater together?

They require vastly different currents to function properly, and in a series circuit, if one component fails, the entire circuit stops working.

What is Joule's law of heating, and what equation represents the heat ($H$) generated?

Joule's law states that heat produced in a resistor is directly proportional to the square of current ($I^2$), resistance ($R$), and time ($t$): $H = I^2 R t = \frac{V^2}{R} t$.

Why are incandescent electric bulbs filled with inert gases like nitrogen and argon?

Inert gases extend the life of the tungsten filament by preventing chemical oxidation at high operating temperatures.

What is electric power, and what is its SI unit?

Electric power ($P$) is the rate at which electric energy is dissipated or consumed in an electric circuit; its SI unit is the watt ($\text{W}$).

What formulas can be used to calculate electric power ($P$)?

$$P = I^2 R = \frac{V^2}{R} = \frac{W}{t} = \frac{E}{t}$$

What is the commercial unit of electrical energy, and how many joules ($\text{J}$) does it equal?

The commercial unit is the kilowatt hour ($\text{kWh}$), also called a 'unit', and $1\,\text{kWh} = 3.6 \times 10^6\,\text{J}$.

In Activity 11.3, what effect does doubling the length of the wire have on current, as measured by the ammeter?

Doubling the length of the wire decreases the ammeter reading to half of its original value.