Electric and Gravitational Fields

What is a field in physics?

A region where a force is exerted on objects due to a physical quantity like mass or charge.

What causes electric fields?

Electric fields are caused by electric charges.

What is Coulomb’s Law formula?

F = 9 × 10^9 x Q1Q2 / r^2, where 9 × 10^9 Fm^-1 (k) is Coulomb’s constant.

How is electric field strength (E) defined?

E = F / q, where F is the force and q is the charge.

What is gravitational field strength (g)?

The force per unit mass on a small test mass placed at a point, caused by mass.

What is the relationship between gravitational force and mass according to Newton’s Law of Universal Gravitation?

F = G x M1M2 / r^2, where G is the gravitational constant.

Define the Inverse Square Law in the context of electric and gravitational forces.

Both electric and gravitational forces decrease with the square of the distance (1/r^2).

What does Newton’s Shell Theorem state?

Outside a uniform spherical mass, the gravitational field behaves as if all mass is concentrated at a single point at the centre.

How does gravitational field strength outside a sphere relate to mass and distance?

g = GM / r^2, where M is the total mass of the sphere and r is the radial distance from the centre.

What do field lines represent?

Imaginary lines that show the direction of force in a field.

How do electric field lines behave around charges?

They point away from positive charges and toward negative charges.

What is an equipotential surface?

A surface where the potential is the same at all points.

What can be said about work done on an equipotential surface?

The work done is zero, since moving along the surface does not change potential energy.

What is the formula for electric potential (V) at a point due to a charge q?

V = kq / r.

What is the gravitational potential (Φ) formula at a point due to a mass M?

Φ = −GM / r, which is always negative.

What is the formula for gravitational potential energy (ΔUP) change?

ΔUP = mgΔh, where g is constant over small height changes.

What should be used for gravitational potential energy over large distance changes?

Use U_P = − GMm / r instead of mgΔh.