FUNDAMENTALS OF ELECTRICITY

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• Q1: Define Electric Current. Write the formula.
  Ans: Electric current is the flow of electric charge through a conductor.
  It is denoted by (I).
  
  Formula:
  
  I = Q / t
  
  Where:
  I = Current
  Q = Charge
  t = Time
• Q2: Define Ampere.
  Ans: Ampere is the unit of electric current.
  One ampere is the current when one coulomb of charge flows in one second.
  
  1 A = 1 C / s
• Q3: Define Electric Charge.
  Ans: Electric charge is the quantity of electricity present in a body.
  It is denoted by (Q) and measured in coulomb (C).
• Q4: Define Molecules.
  Ans: A molecule is the smallest particle of a substance that can exist independently and retains its properties.
• Q5: Define Compounds.
  Ans: A compound is a substance formed by the chemical combination of two or more elements in fixed proportions.
• Q6: Define Atom.
  Ans: An atom is the smallest unit of an element that takes part in a chemical reaction.
• Q7: What is Electron Theory?
  Ans: Electron theory states that electric current is produced due to the movement of free electrons in a conductor.
• Q8: What does an Atom consist of?
  Ans: An atom consists of the following particles:

  • ➔ Protons
  • ➔ Neutrons
  • ➔ Electrons
• Q9: What is an Electron?
  Ans: An electron is a negatively charged particle that revolves around the nucleus of an atom.
• Q10: What is a Proton?
  Ans: A proton is a positively charged particle present in the nucleus of an atom.
• Q11: What is a Neutron?
  Ans: A neutron is a neutral particle (no charge) present in the nucleus of an atom.
• Q12: What are Electron Shells? Name the shells.
  Ans: Electron shells are the paths or energy levels in which electrons revolve around the nucleus.
  
  The shells are:

  • ➔ K Shell
  • ➔ L Shell
  • ➔ M Shell
  • ➔ N Shell
• Q13: What are Valence Electrons?
  Ans: Valence electrons are the electrons present in the outermost shell of an atom.
  They take part in chemical reactions.
• Q14: What are Free Electrons?
  Ans: Free electrons are the electrons that are loosely bound and can move freely within a conductor.
• Q15: Define Columb.
  Ans: Coulomb is the unit of electric charge.
  One coulomb is the charge transported by one ampere current in one second.
  
  1 C = 1 A × s
• Q16: Define Conductors. Give Examples.
  Ans: Conductors are materials that allow electric current to pass through them easily.
  
  Examples:

  • ➔ Copper
  • ➔ Aluminium
  • ➔ Silver
• Q17: Define Insulators. Give Examples.
  Ans: Insulators are materials that do not allow electric current to pass through them.
  
  Examples:

  • ➔ Rubber
  • ➔ Plastic
  • ➔ Glass
• Q18: Define Semi-Conductors. Give Examples.
  Ans: Semi-conductors are materials that have conductivity between conductors and insulators.
  
  Examples:

  • ➔ Silicon
  • ➔ Germanium
• Q19: Define Resistors. Give Examples.
  Ans: Resistors are components used to oppose or limit the flow of electric current in a circuit.
  
  Examples:

  • ➔ Carbon resistor
  • ➔ Wire wound resistor
• Q20: Define Resistance.
  Ans: Resistance is the opposition offered by a material to the flow of electric current.
  It is denoted by (R) and measured in ohms (Ω).
• Q21: Define Ohm.
  Ans: Ohm is the unit of resistance.
  A conductor has resistance of one ohm if one volt produces one ampere current through it.
  
  1 Ω = 1 V / A
• Q22: Define Direct Current (D.C).
  Ans: Direct current (D.C) is the type of electric current that flows in only one direction.
  It is constant in magnitude and direction.
• Q23: Define Alternating Current (A.C).
  Ans: Alternating current (A.C) is the type of electric current that changes its direction and magnitude periodically.
• Q24: Define Potential.
  Ans: Electric potential is the amount of work done in bringing a unit positive charge from infinity to a point in an electric field.
• Q25: Define Potential Difference.
  Ans: Potential difference is the difference in electric potential between two points in a circuit.
  It causes the flow of electric current.
• Q26: Define Voltage.
  Ans: Voltage is another name for potential difference between two points in an electric circuit.
• Q27: Define Volte.
  Ans: Volt is the unit of potential difference (voltage).
  One volt is the potential difference when one joule of work is done to move one coulomb of charge.
  
  1 V = 1 J / C
• Q28: What is Ohm’s Law?
  Ans: Ohm’s Law states that current flowing through a conductor is directly proportional to the voltage across it, provided temperature remains constant.
  
  Formula:
  
  V = I × R
• Q29: If the hot resistance of a 110 volt carbon filament lamp is 250 ohms, find the Current.
  Ans: Given:
  Voltage (V) = 110 V
  Resistance (R) = 250 Ω
  
  Formula:
  I = V / R
  
  Solution:
  I = 110 / 250
  I = 0.44 A
  
  Answer: Current = 0.44 A
• Q30: Calculate the resistance of a 100 watt lamp if the current of 500mA results from a supplied voltage of 200V.
  Ans: Given:
  Voltage (V) = 200 V
  Current (I) = 500 mA = 0.5 A
  
  Formula:
  R = V / I
  
  Solution:
  R = 200 / 0.5
  R = 400 Ω
  
  Answer: Resistance = 400 Ω
• Q31: How much voltage will be measured across the resistor from 8mA current through 30k-ohm resistance?
  Ans: Given:
  Current (I) = 8 mA = 0.008 A
  Resistance (R) = 30 kΩ = 30000 Ω
  
  Formula:
  V = I × R
  
  Solution:
  V = 0.008 × 30000
  V = 240 V
  
  Answer: Voltage = 240 V
• Q32: What is the Law of Resistance?
  Ans: The law of resistance states that the resistance of a conductor depends on the following factors:

  • ➔ Length of the conductor
  • ➔ Cross-sectional area
  • ➔ Nature of material
  • ➔ Temperature
• Q33: Define Specific Resistance.
  Ans: Specific resistance is the resistance of a material having unit length and unit cross-sectional area.
• Q34: Define Resistivity.
  Ans: Resistivity is the property of a material that shows how much it opposes the flow of electric current.
  It is denoted by (ρ).
  
  Formula:
  
  ρ = R × A / L
• Q35: What is an Electric Circuit?
  Ans: An electric circuit is a closed path through which electric current flows from a source to a load and back to the source.
• Q36: Define Series Circuit.
  Ans: A series circuit is a circuit in which components are connected one after another in a single path.
  The same current flows through all components.
• Q37: Define Parallel Circuit.
  Ans: A parallel circuit is a circuit in which components are connected across the same two points.
  Different current flows through each branch.
• Q38: Three resistors of 25, 40 and 75 ohms are connected in series. Find the equivalent resistance.
  Ans: Given:
  R₁ = 25 Ω
  R₂ = 40 Ω
  R₃ = 75 Ω
  
  Formula (Series):
  R = R₁ + R₂ + R₃
  
  Solution:
  R = 25 + 40 + 75
  R = 140 Ω
  
  Answer: Equivalent Resistance = 140 Ω
• Q39: Two resistors of 12 and 8 ohms are connected in parallel. Find equivalent resistance.
  Ans: Given:
  R₁ = 12 Ω
  R₂ = 8 Ω
  
  Formula (Parallel):
  1 / R = 1 / R₁ + 1 / R₂
  
  Solution:
  1 / R = 1/12 + 1/8
  1 / R = (2 + 3) / 24
  1 / R = 5 / 24
  
  R = 24 / 5
  R = 4.8 Ω
  
  Answer: Equivalent Resistance = 4.8 Ω
• Q40: Three resistors of 30, 40 and 70 ohms are connected in parallel. Find the total resistance.
  Ans: Given:
  R₁ = 30 Ω
  R₂ = 40 Ω
  R₃ = 70 Ω
  
  Formula:
  1 / R = 1 / R₁ + 1 / R₂ + 1 / R₃
  
  Solution:
  1 / R = 1/30 + 1/40 + 1/70
  
  Taking LCM = 840:
  1 / R = (28 + 21 + 12) / 840
  1 / R = 61 / 840
  
  R = 840 / 61
  R ≈ 13.77 Ω
  
  Answer: Total Resistance ≈ 13.77 Ω
• Q41: What is a Capacitor or a Condenser?
  Ans: A capacitor (or condenser) is a device used to store electric charge or electrical energy in an electric field.
• Q42: Define Capacitance.
  Ans: Capacitance is the ability of a capacitor to store electric charge.
  
  Formula:
  
  C = Q / V
  
  Where:
  C = Capacitance
  Q = Charge
  V = Voltage
• Q43: Define Farad.
  Ans: Farad is the unit of capacitance.
  A capacitor has a capacitance of one farad if it stores one coulomb of charge at one volt potential difference.
  
  1 F = 1 C / V
• Q44: What is Dielectric?
  Ans: A dielectric is an insulating material placed between the plates of a capacitor to increase its capacitance.
• Q45: What are Capacitors in Series?
  Ans: Capacitors in series are connected one after another in a single path.
  
  Formula:
  
  1 / C = 1 / C₁ + 1 / C₂ + 1 / C₃
• Q46: What are Capacitors in Parallel?
  Ans: Capacitors in parallel are connected across the same two points.
  
  Formula:
  
  C = C₁ + C₂ + C₃
• Q47: Define Work.
  Ans: Work is done when a force moves an object through a distance.
  
  Formula:
  
  Work = Force × Distance
• Q48: Define Electric Power. Write the formula.
  Ans: Electric power is the rate at which electrical energy is consumed or produced in a circuit.
  
  Formula:
  
  P = V × I
  
  Where:
  P = Power
  V = Voltage
  I = Current
• Q49: Define Watt.
  Ans: Watt is the unit of electric power.
  One watt is the power when one ampere current flows under one volt potential difference.
  
  1 W = 1 V × 1 A
• Q50: Define Mechanical Power.
  Ans: Mechanical power is the rate of doing mechanical work.
  
  Formula:
  
  Power = Work / Time
• Q51: Define Energy.
  Ans: Energy is the capacity to do work.
  It is measured in joules (J).
• Q52: What is BOTU?
  Ans: BOTU (Board of Trade Unit) is the unit of electrical energy.
  It is also called one kilowatt-hour (kWh).
  
  1 BOTU = 1 kWh
• Q53: A potential difference of 20 volts is applied across a resistor of 2.5 ohms. calculate the current and power dissipated.
  Ans: Given:
  Voltage (V) = 20 V
  Resistance (R) = 2.5 Ω
  
  Step 1: Find Current
  Formula:
  I = V / R
  
  I = 20 / 2.5
  I = 8 A
  
  Step 2: Find Power
  Formula:
  P = V × I
  
  P = 20 × 8
  P = 160 W
  
  Answer:
  Current = 8 A
  Power = 160 W
• Q54: A motor takes an average current of 32 A at 440V. Find the power absorbed in KW. How many B.O.T units are used in 6 hours?
  Ans: Given:
  Current (I) = 32 A
  Voltage (V) = 440 V
  Time = 6 hours
  
  Step 1: Find Power
  Formula:
  P = V × I
  
  P = 440 × 32
  P = 14080 W
  P = 14.08 kW
  
  Step 2: Find Energy (BOT Units)
  Formula:
  Energy = Power × Time
  
  Energy = 14.08 × 6
  Energy = 84.48 kWh
  
  Answer:
  Power = 14.08 kW
  Energy = 84.48 BOT Units
• Q55: What is the Heating effect of Current?
  Ans: The heating effect of current is the production of heat when electric current flows through a conductor due to resistance.
• Q56: What is a Calorie?
  Ans: A calorie is a unit of heat energy.
  It is the amount of heat required to raise the temperature of 1 gram of water by 1°C.
• Q57: What is Joule’s Law?
  Ans: Joule’s Law states that the heat produced in a conductor is directly proportional to the square of current, resistance, and time.
  
  Formula:
  
  H = I² × R × t
• Q58: What is an Inductor?
  Ans: An inductor is an electrical component that stores energy in the form of a magnetic field when current flows through it.
• Q59: What are R.L.C Circuits?
  Ans: R.L.C circuits are electrical circuits that contain:

  • ➔ Resistor (R)
  • ➔ Inductor (L)
  • ➔ Capacitor (C)

  These circuits are used to study the behavior of alternating current.
• Q60: Define Impedance.
  Ans: Impedance is the total opposition offered by a circuit to the flow of alternating current (A.C).
  It is denoted by (Z) and measured in ohms (Ω).
• Q61: What is the Impedance Triangle?
  Ans: The impedance triangle shows the relationship between resistance, reactance, and impedance in an A.C circuit.
  
  It consists of:

  • ➔ Resistance (R)
  • ➔ Reactance (X)
  • ➔ Impedance (Z)
• Q62: What is Phase Angle?
  Ans: Phase angle is the angle between voltage and current in an A.C circuit.
  It shows the difference in their timing.
• Q63: Name the phases of electricity.
  Ans: The phases of electricity are:

  • ➔ Single Phase System
  • ➔ Two Phase System
  • ➔ Three Phase system
• Q64: Define Single Phase System.
  Ans: A single phase system uses only one alternating voltage to supply power.
• Q65: Define 2 advantages of Single Phase System.
  Ans: Following are the advantages of Single Phase System:

  • ➔ It is cheaper to install.
  • ➔ It is suitable for small loads.
• Q66: Define Poly Phase System.
  Ans: A poly phase system uses more than one alternating voltage or current. It includes Two Phase System and Three Phase system.
• Q67: Define Two Phase System.
  Ans: A two phase system uses two voltages that are 90 degrees apart.
• Q68: Define 2 advantages of Two Phase System.
  Ans: Following are the advantages of Two Phase System:

  • ➔ It provides smoother power than single phase.
  • ➔ It can run medium-sized motors efficiently.
• Q69: Define Three Phase System.
  Ans: A three phase system uses three voltages that are 120 degrees apart.
• Q70: Define 2 advantages of Three Phase System.
  Ans: Following are the advantages of Three Phase System:

  • ➔ It is more efficient for power transmission.
  • ➔ It runs heavy motors smoothly.
• Q71: What is the Power Factor?
  Ans: Power factor is the ratio of real power to apparent power in an A.C circuit.
  
  Formula:
  
  Power Factor = cosθ
• Q72: What is the difference between a Cell and a Battery?
  Ans: The difference is as follows:

  • ➔ A cell is a single unit that produces electricity.
  • ➔ A battery is a combination of two or more cells connected together.
• Q73: Name the types of Cells.
  Ans: The types of cells are:

  • ➔ Primary Cells
  • ➔ Secondary Cells
• Q74: What is a Primary Cell?
  Ans: A primary cell is a type of cell that cannot be recharged after use.
  It is used only once.
• Q75: State the types of Primary Cells.
  Ans: Types of primary cells are:

  • ➔ Voltaic Cell
  • ➔ Carbon Zinc Dry Cell
  • ➔ Mercury Cell
  • ➔ Lithium Cell
• Q76: What is a Secondary Cell?
  Ans: A secondary cell is a type of cell that can be recharged and used again.
• Q77: State the types of Secondary Cells.
  Ans: Types of secondary cells are:

  • ➔ Lead Acid Battery
  • ➔ Edison Cell
• Q78: What is a Voltaic cell?
  Ans: A voltaic cell is a device that converts chemical energy into electrical energy through a chemical reaction.
• Q79: What is Carbon Zinc Dry Cell?
  Ans: A carbon zinc dry cell is a primary cell that uses zinc as anode and carbon as cathode, with a paste electrolyte.
• Q80: What is a Mercury Cell?
  Ans: A mercury cell is a primary cell that uses mercury oxide and zinc to produce a stable voltage.
• Q81: Define Anode.
  Ans: Anode is the electrode where oxidation takes place and current enters into the cell.
• Q82: Define Cathode.
  Ans: Cathode is the electrode where reduction takes place and current leaves the cell.
• Q83: What is a Lithium Cell?
  Ans: A lithium cell is a primary cell that uses lithium metal and provides high energy and long life.
• Q84: What is Lead Acid Battery?
  Ans: A lead acid battery is a secondary cell that uses lead plates and sulfuric acid as electrolyte.
  It can be recharged and used multiple times.
• Q85: Define Electrolyte.
  Ans: An electrolyte is a substance that allows the flow of electric current through it by the movement of ions.
• Q86: State any two uses of Lead Acid Battery.
  Ans: Uses of lead acid battery:

  • ➔ Used in automobiles (cars, motorcycles)
  • ➔ Used in UPS and backup power systems
• Q87: What is an Edison Cell?
  Ans: An Edison cell is a secondary cell that uses nickel and iron plates with an alkaline electrolyte.
• Q88: State two uses of Edison Cell.
  Ans: Uses of Edison cell:

  • ➔ Used in railway signaling
  • ➔ Used in industrial backup systems
• Q89: Define matter. Write its states.
  Ans: Matter is anything that has mass and occupies space.
  
  States of matter:

  • ➔ Solid
  • ➔ Liquid
  • ➔ Gas