Introduction to Electricity

• Electricity involves current and voltage and the study of electric charges and their movement.

Atomic Structure

• Atoms contain a positively charged nucleus with negatively charged electrons that revolve around it
• Valence electrons in metals are free to move within conductors, forming electric current

Charge

• Charge is an intrinsic property of matter that allows it to exert electromagnetic force
• Like charges repel each other, while opposite charges attract

Conductors and Insulators

• Conductors offer less opposition to current flow, while insulators offer more

Electric Potential and Potential Difference

• Electric potential at a point is the work needed to bring a unit positive charge from infinity to that point
• Potential difference between two points is the difference in electric potentials between those points.

Electric Current

• Electric current (I) refers to the flow of electric charges, defined as charge per unit time: I = Q/t

Electron Sea Model

• Electric current in solid conductors results from the drift of free electrons able to jump to neighboring atoms.
• The model includes positive metal ions and an "electron cloud" that does not belong to any metal ion

Drift Velocity of Electrons

• Drift velocity is the average velocity an electron attains inside a metallic conductor when influenced by an electric field due to a potential difference

Battery

• A cell serves as a source of potential difference, generated internally through chemical reactions
• At the anode: Cu(s) → Cu2+(aq) + 2e-
• At the cathode: Ag(aq) + 2e- → 2Ag(s)
• A battery is a combination of multiple cells

Electric Circuit

• An electric circuit is a closed-loop path that allows current to flow
• A circuit diagram represents an electric circuit using symbols
• An ammeter measures current, a voltmeter measures voltage, and resistance opposes current flow.

Resistance and Ohm's Law

• Ohm's Law: The current through an ohmic conductor is directly proportional to the applied potential difference across its ends

Resistance

• Resistance measures the opposition to current flow in an electric circuit

Factors Affecting Resistance

• Length: Resistance is directly proportional to the conductor's length
• Nature: Resistance is directly proportional to the material's nature
• Temperature: Resistance is directly proportional to the conductor's temperature
• Cross-sectional area: Resistance is inversely proportional to the conductor's cross-sectional area

Resistivity

• Resistivity is the electrical resistance of a substance with unit length and unit cross-sectional area

Ohmic and Non-Ohmic Resistors

• Ohmic resistors follow Ohm's Law, whereas non-Ohmic resistors do not.

Superconductors

• Superconductors are conductors that offer zero resistance to the flow of current

Combination of Resistors

• Resistors in series carry the same current
• Resistors in parallel have the same potential difference applied to them

Equivalent Resistance

• For series circuits, Req = R1 + R2
• For parallel circuits, 1/Req = 1/R1 + 1/R2

EMF and Terminal Voltage

• EMF is the potential difference between terminals of a cell when no current flows
• Terminal voltage refers to the potential difference when current is flowing

Heating Effect of Current

• Joule's Law describes heating effect of current
  • Heat (H) ∝ square of the current (I)
  • H ∝ Resistance of the circuit
  • H ∝ Time (t) for which current flows

Electric Power

• Electric power is the rate of doing work or energy consumption, P = W/t
• The S.I. unit for power is the Watt (W).
• 1 Watt is consumed when 1 A of current flows at a potential difference of 1 V
• Commercial unit of electrical energy is kilowatt-hour (kWh) = 3.6 × 10^6 J
• 1 kilowatt-hour is used by 1kW of power for 1 hour
• Power represented as P = I²R and P = V²/R