7.01 Quiz: Static Electricity MCQ Questions and Answers

Study Notes

Electric Charge

Electric charge (Q or q) indicates if a body has more or less electrons than protons.
The unit of charge is coulomb (C).

Atomic Structure

An atom is made up of three particles: protons, neutrons, and electrons.
Protons and neutrons are located in the centre of the atom, and electrons orbit the nucleus.

Charge Interactions

Like charges repel each other, unlike charges attract each other.
Rubbing cloth and polythene causes the polythene to become negatively charged, and rubbing cloth against perplex causes the perplex to become positively charged.
This demonstrates forces between charges.

Conductors and Insulators

A conductor is any substance through which electric charge can flow.
An insulator is any substance through which electric charge cannot flow.
All static charges reside on the outside of a conductor.
Static charge on a conductor tends to accumulate where the conductor is most pointed.
Point discharge occurs at a very sharp point due to charge density, resulting in a strong electric field being created.

Ions and Neutrality

Ions are both attracted and repelled, neutralising the object.
This can be demonstrated by showing the effect of the ‘electric wind’ created on a naked flame.

Gold Leaf Electroscope

The gold leaf electroscope is used to detect small charges, estimate the size of a charge, identify the sign of the charge, and distinguish between a conductor and insulator.
It consists of multiple components, most importantly a thin gold leaf placed close to a metal rod.
If these are both charged with the same sign, they repel each other.

Coulomb's Law

The force between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them.
Unit = newton (N)
This is an example of an inverse square law.
The size of the force is the same on each body, and the force is along the line between them.

Factors Affecting Electrostatic Force

One of the factors affecting the size of the electrostatic force is the permittivity (ε) of the medium surrounding the charges.
If the permittivity is low, the force is big; permittivity and force are inversely proportional.
The force is greatest when the charges are in a vacuum.

Electric Field

An electric field is any region of space where a static electric charge experiences a force other than the force of gravity.
An electric field line is the line along which a positive charge would move if placed in the electric field.
The electric field strength (E) at a point in an electric field is the force per unit positive charge at that point.
S.I. Unit = newton per coulomb (N C-1) or volt per meter (V/m)

Description

Learn about electric charge, atoms, and the behavior of charged particles like protons, neutrons, and electrons. Understand how like charges repel and unlike charges attract each other, along with common methods of generating static electricity.