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Static Electricity | O Level Physics 5054 & IGCSE Physics 0625 | Detailed Free Notes To Score An A Star (A*)

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Topics:

  • Static Electricity
    • Electrostatic Phenomenon
    • Laws of Electrostatics
    • Charge
    • Electric Field
    • Force Lines
    • Charging and discharging through Induction
    • Electroscope
    • Electrical Conductors and Insulators
    • Charging Uses and Hazard
  • Current Electricity
    • Current
    • Electromotive force (EMF)
    • Potential difference (PD)
    • Graphs
    • Designing Battery
    • Resistance
    • Ohm’s Law
    • Resistivity
    • Resistance in series and parallel
    • LDR

Static Electricity:

Electrostatic Phenomenon:

Some objects get charge by rubbing with each other. This process is called Electrostatic phenomenon.

Laws of Electrostatics:

  • Same charges repel each other.
  • Opposite charges attract each other.

Charge (Q):

  • The current flowing in a specific point of circuit in unit time is called charge.
  • SI UNIT: Coulomb (C)
  • 1 Coulomb = 1 ampere current flowing in circuit in 1 second
  • Q = IT where Q is charge, I is the current and T is time in seconds.

Electric Field:

The region in which a positive charge is influenced by a force is called an electric field.

Force Lines:

The force/ field lines go out of a positive charge and into a negative charge.

Important Point:

  • Current flows from high potential to low potential.
  • Earth Provides 0 potential. Earthing means to connect to earth to neutralize charge.

Charging through Induction:

Charging happens due to friction on some materials:

  • Glass rod is charged with silk. It has positive charge.
    • It will attract an uncharged pith ball
  • Ebonite rod is charged with fur and has negative charge.
    • It will attract an uncharged pith ball
  • If both ebonite rod and glass rod are used to attract, they will cancel each other’s forces and the ball will attract less.

Methods of Charging through Electrostatic Induction:

Induction charging happens when electrons move. They carry negative charge. If electrons are reduced, we get positive charge.

Two Metal spheres:

  • Place the metal spheres on insulator so that the charge won’t leak.
  • Bring charged rod near one sphere. Let us say the rod has positive charge
  • The negative charges will attract and the positive (Same) charges will repel.
  • Bring the other sphere closer with the rod still present.
  • The positive charges will be pushed to the other sphere and the negative will be attracted to the first sphere. (see diagram for placement).
  • Remove the spheres first and then the rod.
  • Removing rod first will make the spheres neutral again.

Single Sphere:

  • Place the sphere on insulator.
  • Bring charged rod near to the sphere.
  • Like charges repel and unlike will attract.
  • Earth the other side and neutralize those charges.
  • Remove earth connection
  • Remove rod.
  • Only one charge is left, and sphere is charged.

Discharging Spheres:

Touch or Earth to discharge. Make sure they are not on insulators when discharging.

Electroscope:

An electroscope is a device that is commonly used in the labs. It has three uses:

  • To check if something is charged or not
  • To check if something has positive charge or not
  • To check if something has negative charge or not

To check if something is charged or not:

  • Bring the rod near the brass cap.
  • Opposite charges are attracted, and same charges will travel down to the gold leaf.
  • The gold leaf ends will have the same charges and hence, they will repel.
  • This shows that the rod is charged.

To check if something is positively charged or not:

  • Charge the electroscope with a negative rod.
  • Earth will remove the negative charge and leave the positive charge.
  • Positive charge would spread to balance on surface in brass cap and gold leaf.
  • Bring your test rod near.
  • If the repulsion increases, it means more positive charge has travelled down.
  • The rod has to be positively charged in order to repel positive charge down to the gold leaf.

To check if something is negatively charged or not:

  • Similar to positive charge, charge the electroscope with negative rod to give it initial negative charge.
  • If the test rod has negative charge, it will cause negative charge to travel down to gold leaf and the repulsion would increase.

Electrical Conductors and Insulators:

Conductors:

Materials that allow current to pass through are known as conductors. For example: metals

Insulators:

Materials which prevent the passage of electricity are known as insulators. For example: plastic, wood

Charging Use and Hazard:

  • Electrical Charging could be hazardous for example in lighting
  • It has benefits for example in photocopier, electrostatic precipitator

Current Electricity:

Current:

  • Current is the rate of flow of charge.
  • SI UNIT: ampere
  • Measured using an ammeter (Always connected in series)
  • Q = IT
  • We use ammeter with bigger range when we have circuits with more current. Ammeter with smaller ranges can measure in more decimals and are hence, more accurate.

Electromotive Force (EMF):

  • Electromotive force is defined as the work done or energy converted from non-electrical to electrical form when one coulomb positive charge flows through a circuit.
  • EMF is measured across the battery in parallel.
  • SI UNIT: Volt

Potential Difference (PD):

  • Potential difference is the amount of work done or energy converted from electrical to non-electrical form when one coulomb positive charge flows between two points.
  • Measured across two points in parallel.
  • PD across straight wire is O.
  • SI UNIT: Volt
  • We use potentiometers/ voltmeters with bigger range when we have circuits with more voltage. With smaller ranges, we can measure in more decimals and are hence, more accurate.

Graphs:

The graphs of voltage against current (with resistance info) for some common material are given below:

Designing Battery:

EMF is the total voltage that a battery supply. Measuring EMF while designing a battery is the best way to design. Also, battery is designed in parallel rather than series.

Resistance:

  • Resistance is the property of material that restricts the flow of free electron.
  • SI UNIT: Ohms (Ω)
  • Symbol r
  • Resistance is PD/I or voltage/ current.

Ohm’s Law:

  • The current is directly proportional to potential difference under controlled conditions such as temperature.
  • The materials that obey ohm’s law are called Ohmic material.
  • V = IR

Resistivity:

  • Resistance depends on two main factors:
    • Resistance is directly proportional to Length (l)
    • Resistance is inversely proportional to Surface Area (A)
    • r ∝ L/A
  • r = R(L/A)
  • where R is the resistivity
  • SI UNIT: Ohm meters (Ω m)

Resistance in Circuits:

Series:

Resistance in series circuit is measured by adding all the resistances across all components. r = r1 + r2 + …. + rn

Parallel:

Resistance in parallel circuits is calculated by the following formula: 1/r = = 1/r1 + 1/r2 + … + 1/rn

LDR:

Light dependent resisters or LDRs (photoreceptor) are components that decrease in resistance as light increases.

Hunain Zia

Hunain Zia has previously achieved considerable success in the high-school educational stream, gaining a massive 154 Total A Grades and 7 Major Distinctions, a process in which he broke/ set 11 different world records, including the most A grades ever achieved, most subjects ever appeared in, most distinctions, gaining distinctions across two separate boards (Pearson Edexcel and CAIE) within the same year/ ever, and even 19 hours of constant examination. All records stand intact today. Hunain pursued his Honors Accounting Degree from the prestigious Bentley University, and then completed an LLB (in Honors) from University of London. Currently, he manages multiple social and commercial projects, has founded digital streams and works tirelessly in the education sector.

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