Physics Unit 4

A capacitor is a pair of conducting plates separated by an
insulator. If a potential difference is placed across the plates,
they acquire equal and opposite charges.

Farad (F) = C/V

The force experienced per unit charge (Volts per meter or newtons per coulomb).

The force experienced per unit mass (Newtons per kilogram or metres per second squared)

Each planet moves along an eliptical path, with the sun located at one focus.

The line joining a planet to the centre of the sun sweeps out equal areas in equal times.

The square of the period of the planet's motion is proportional to the semi major axis cubed $(T^2\propto r^3)$. In circular orbits, the semi major axis may be approximated as the mean distance of the planet to the sun.

Matter which we can't see or detect via any radiation, but can infer its existence from gravitational observations.

Magnetic field stength. It is measured in Tesla, and denoted by B

The potential difference formed when a current carrying wire is paced at a right angle to the field direction, so that a potential difference is formed across the radius of the wire

Using Fleming's left hand rule for motors (motor cars drive on the left), or Fleming's right hand rule for generators, where I is the direction of conventional current

Using Maxwell's right hand grip rule, where the thumb is pointing in the direction of conventional current flow

Positive to negative

Negative to positive

$\Phi$, the product of the area enclosed by a coil and the magnetix flux density ( Tesla meter squared)

The magnetic flux multiplied by the number of coils

The rate emf induced in a coil is equal to the rate of change of flux linkage $E=\frac{-\Delta (N\Phi)}{\Delta t}$

The direction of current from an induced emf is in the opposite direction to change in flux linkage

I, the sum of the masses mutiplied by their distance from the centre squared

$I=\frac{2}{5}mr^2$

$I=\frac{2}{3}mr^2$

The rate of change of angular velocity

The rate of change of angular momentum $(\tau=Ia)$

J, where $J=I\omega$

The total angular momentum in a system remains consant provided no external torque acts on the system

$p=p_0-\frac{1}{2}\rho v^2$

If $v=H_0D$, and $v=\frac{D}{t}$, then $\frac{1}{t}=H_0$

A paticle of mass m may be imagined at the edge of the universe. if $r_u$ is the radius of the universe, then its recessional velocity is $H_0r_u$.

If the expansion comes to a stop eventually, then it must have 0 energy at infinite distance, so its gravitational energy must equal its kinetic energy

Its gravitation energy is the product of the mass of the particle and the mass of the universe. An expression for the mass of the universe may be found, and this may then be used to find the critical density

$e=\sqrt{\frac{h}{H}}$$