Electric Field and Potential

Electric Field and Potential

• Electric field behaves as if all the charge creating it is at a point in the centre of the sphere when observed from outside.
• Electric potential is defined as the work done in bringing a test unit positive charge from infinity to a point in the electric field.
• The potential of a charge at infinity is always defined to be zero.
• If the charge creating the field is positive, work must be done to bring a test positive charge in from infinity, as like charges repel.
• If the charge creating the field is negative, the work done to bring in a test positive charge from infinity is negative, as unlike charges attract.

Variation of Electric Field with Distance

• Electric field strength varies with distance for a point charge, a capacitor, and a hollow charged sphere.
• Negatively charged point charges and spheres would give negative versions of the same graph.
• The potential due to a positive charge is positive, while the potential due to a negative charge is negative.

Point Charge

• Electric field strength declines with distance following an inverse square law (E ∝ 1/r²).
• Electric potential is a measure of the potential energy per unit charge.
• Potential energy on a charge due to a potential V is: P.E. = qV.

Field Theory and Electric Fields

• Field theory is a model for explaining forces that act at a distance, such as electric, magnetic, or gravitational forces.
• Electric fields are used to explain the forces that act between charges.
• Forces on charges can be represented by drawing field lines (lines with arrows).
• The closer together the lines are, the stronger the field.
• Field lines point in the direction a positive test charge would move.

Charge and Electric Forces

• There are two types of charge: positive charge (carried by particles such as protons) and negative charge (carried by particles such as electrons).
• The unit of charge is the coulomb (C).
• Charge comes in discrete packets, and it is quantized.
• The smallest unit of charge is 1.6 × 10⁻¹⁹C, the size of the charge on an electron or proton.
• Any object carrying a charge will experience a force when in the presence of another body also carrying a charge, following Coulomb's Law.
• Like charges repel, while unlike charges attract.