Electricity

Static Electricity

  1. What is similar about a spark and a lightning bolt?Both are sudden discharges of static electricity, where electrons rapidly move to balance charge differences.

  2. Why do charged objects attract neutral objects?Charged objects cause charge separation in neutral objects, attracting opposite charges due to electron redistribution.

  3. What is the electrostatic series?A ranking of materials based on their tendency to gain or lose electrons. Higher-ranked materials lose electrons (positively charged); lower-ranked gain electrons (negatively charged) when rubbed together.

  4. Conductors vs. Insulators:

    • Conductors allow free electron movement (e.g., metals).

    • Insulators resist electron flow (e.g., rubber, plastic).

  5. Why can you get a charge by shuffling feet on a carpet?Friction transfers electrons between the carpet and your feet, building up static charge.

  6. Law of attraction and repulsion:

    • Like charges repel;

    • Opposite charges attract.

  7. Difference between negatively and positively charged objects:

    • Negatively charged: more electrons than protons.

    • Positively charged: fewer electrons than protons.

  8. What does grounding mean?Grounding allows excess charge to flow into the Earth, neutralizing objects (positively charged objects gain electrons; negatively charged lose electrons).

  9. Charging methods:

    • Induction: Charging without contact by bringing a charged object near a conductor.

    • Friction: Charging by rubbing two materials together.

    • Contact: Charging by touching a charged object to a neutral one.

  10. What is lightning?A massive static discharge occurring when charge imbalances build up from friction between air particles, producing a flash of light and heat.

Current Electricity

  1. Definitions:

  • Current: Flow of electric charge (amperes).

  • Circuit: Closed path for current flow.

  • Charge: Amount of electric charge (coulombs).

  • Potential difference (Voltage): Energy per unit charge (volts).

  • Resistance: Opposition to current flow (ohms).

  1. Functions of instruments:

  • Ammeter: Measures current.

  • Voltmeter: Measures voltage.

  • Battery: Source of electrical energy.

  • Fuse: Protects circuits by breaking current when too high.

  1. Connecting a voltmeter:A voltmeter is connected in parallel across a bulb to measure potential difference.

  2. Why use insulators for wires?Insulators prevent current leakage and protect against shock.

  3. How does a circuit breaker work?Interrupts current flow on overload or short circuit to prevent damage.

  4. Connecting cells in series:Produces the highest electrical potential.

  5. Voltage with five 1.8V cells in series:Total potential = 1.8V × 5 = 9.0V.

  6. Advantages of series vs. parallel:

  • Series: Increases voltage.

  • Parallel: Increases current and ensures operation if one cell fails.

Current Electricity Calculations

  1. Current needed for a toaster:

  • Resistance of a resistor with 35V and 2A:

  • Resistance remains constant with voltage increase if the resistor is ohmic.

  1. Huge Circuit Analysis:

  • Brightest bulb in a parallel circuit has the fewest bulbs.

  • If a bulb on a branch burns out, others remain unaffected.

  • Adding bulbs decreases intensity due to increased resistance.