Electricity and Circuits Lecture Notes

Flashcards based on lecture notes about electricity and circuits.

What is electric charge?

A physical property of matter causing it to experience force in an electromagnetic field.

What are the two types of electric charge?

Positive and Negative.

What is the SI unit of charge?

Coulomb (C).

What is the formula relating charge (Q), number of electrons (n), and the elementary charge (e)?

Q = +/- ne, where e = -1.6 * 10^-19 C

How does charge behave in a non-conductor?

Resides at a point; there is no flow of electrons.

How does charge behave in a conductor?

Charge can move or flow because of many free electrons.

What is electric current?

The rate of flow of charge (I = Q/t).

What is the SI unit of current?

Ampere (A).

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

Ammeter, connected in series.

Define electric potential.

The amount of work done per unit charge in bringing a test positive charge from infinity to that point (V = W/Q).

What is the SI unit of electric potential?

Volt (V).

Define potential difference.

The work done per unit charge in moving a positive test charge from one point to another.

What instrument measures potential difference, and how is it connected in a circuit?

Voltmeter, connected in parallel.

Define electrical resistance.

The obstruction offered to the flow of current by a conductor.

What is the SI unit of resistance?

Ohm (Ω).

What is Ohm's Law?

The current flowing in a conductor is directly proportional to the potential difference across its ends, provided physical conditions and temperature remain constant (V = IR).

What is electrical conductance?

The reciprocal of resistance (G = 1/R).

What is the unit of conductance?

Ohm^-1 or Siemens.

What is the relationship between the slope of an I-V graph and conductance?

The slope of an I-V graph is conductance.

Give examples of Ohmic conductors.

All metallic conductors.

Give examples of non-Ohmic conductors.

LED, Solar Cell, diode, Transistor, filament of a bulb etc.

List four factors affecting the resistance of a conductor.

Material, length, thickness, and temperature.

Define specific resistance (resistivity).

The resistance of a wire of that material of unit length and unit area of cross-section.

What is the SI unit of resistivity?

Ωm (Ohm metre).

Describe how temperature affects the specific resistance of metals and semiconductors.

Increases for metals, decreases for semiconductors.

Define conductivity.

The reciprocal of specific resistance.

What is the SI unit of conductivity?

Siemen per metre.

Why is copper used for electrical connections?

Negligible resistance.

What materials are resistance wires typically made of?

Nichrome, manganin, constantan etc.

Why is tungsten used for the filament of an electric bulb?

High melting point and high resistivity.

Why is nichrome used as a heating element in appliances?

Very high resistivity that increases with temperature increase.

Define superconductors.

Substances of zero resistance at very low temperature.

What is an electric cell?

A device maintaining a constant potential difference between two terminals via chemical reaction.

Define electromotive force (EMF).

The potential difference between terminals when no current is drawn.

What is the SI unit of EMF?

Volt (V).

What factors affect the EMF of a cell?

Material of the electrodes and Electrolyte used in the cell.

What is terminal voltage?

The potential difference between terminals when current is drawn from the cell.

What is voltage drop in a cell?

The work done per unit charge in carrying a positive test charge through the electrolyte.

Define internal resistance of a cell.

The resistance offered by the electrolyte inside the cell.

How does the surface area of electrodes affect internal resistance?

Inverse relation: increased surface area decreases internal resistance.

How does the distance between electrodes affect internal resistance?

Direct relation: increased distance increases internal resistance.

List the two ways resistors can be combined in a circuit.

Series and Parallel.

In a series combination, what is the equivalent resistance?

The sum of the individual resistances (Rs = R1 + R2 + R3 + …).

In a parallel combination, what is constant?

The potential (voltage).

What are some forms that electrical energy is converted into?

Heat, light, mechanical, and chemical energy.

What is the formula for electrical energy (W) in terms of voltage (V), current (I), and time (t)?

W = VIt

What is the SI unit of electrical energy?

Joule (J).

Define electric power.

The rate at which electric energy is supplied by the source (P = W/t).

What is the formula for electric power (P) in terms of voltage (V) and current (I)?

P = VI

What is the SI unit of electric power?

Watt (W).

List some bigger units of electric power.

Kilowatt, megawatt, and gigawatt.

What is the commercial unit of electrical energy?

Kilowatt-hour (kWh).

What is the relationship between kilowatt-hour and joules?

1 kWh = 3.6 x 10^6 J

How can the resistance of an appliance be calculated from its power and voltage rating?

R = V²/P

How is household consumption of electric energy measured?

In kilowatt-hours (kWh).

What is Joule's Law of Heating?

The heat produced in a wire is proportional to the square of the current, the resistance, and the time (H = I²Rt).