Physics & Maths Tutoring

# Fields

Type of Field

Gravitational

Electric

Force is Between

Objects with mass

Objects with charge

Constant of Proportionality

$G$ is a physical constant

$k = 1 4⁢πε0 ≈9×109$

Note: $ε0$ is a physical constant

Field Strength in a Radial Field

$g = G⁢mr2$

$[g]=N⁢kg-1=m⁢s-2$

$g$ is a vector and is the graviational field strength.

$E = k⁢Qr2$

$[E]=N⁢C-1=V⁢m-1$

$E$ is a vector and is the electric field strength.

Definition of Field Strength

Force per unit mass $g=Fm$

$m$ is a test small test mass.

Force per unit charge $E=FQ$

$Q$ is a test small test charge.

Force in a Radial Field $F= G⁢m1⁢m2 r2$

Always attractive

This is a vector

$F= k⁢Q1⁢Q2 r2$

Can be attractive or repulsive

This is a vector

$V=-G⁢mr$ Jkg-1

Scalar

Always less than zero.

$V=k⁢Qr$ JC-1

Scalar

Sign depends on charges

Definition of Potential

Work done in bringing a unit mass from infinity to the point in the field.

Work done in bringing a unit positive charge from infinity to the point in the field.

Potential Energy

$Ep=V⁢m$ $W=V⁢Q$

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