# Physics

The unit for current is the Amp (A). It is measured with an Ammeter.You can move the Ammeter to different places but the reading will same the same, unless you add more bulbs or batteries.

?
• Created by: Tom Belk
• Created on: 21-05-14 19:51

## Resistance

Electrical appliances waste some energy as heat.

Ohm's Law:

Pd=current x resistance

Resistance= pd/current or R=V/I

Unit for resistance=Ω

1 of 15

## Power Circuits

Energy transferred= current x time x potential difference (itv)

Electrical power= energy transferred/time

Power= current x potential difference

Power= potential difference/ current

Power is measured in Watts or Kilowatts

1 watt of power means that 1 Joule of energy is used every second

2 of 15

## Current

The unit for current is the Amp (A). It is measured with an Ammeter.You can move the Ammeter to different places but the reading will same the same, unless you add more bulbs or batteries.

3 of 15

## Generating Electricity

If a wire is moved across a magnetic field, a current is produced. This is called electromagnetic induction. Induction also occurs if a magnet is moved in a coil of wire, or if a coil of wire rotates in a magnetic field.

In all of these methods of inducing a current, the wire and magnetic field move perpendicular to each other. If they move parallel to each other, no current is induced.

4 of 15

## Efficiency

How electricity is made: Fuel is burned to boil water at a high pressure. The boiling water produces superheated steam. The superheated steam turns a turbine. The turbine rotates a magnet in the generator. The rotating generator generates electricity-chemical, thermal, kinetic and then electrical.

%efficiency=useful energy output/ total energy input x100

5 of 15

## Distance-time graphs

average speed= total distance/ total time

acceleration= speed/ time

6 of 15

## Friction

Friction can cause air resistance or drag. The size of the frictional force equals the applied force unless the applied force is bigger than the maximum value of the frictional force. If this is the case then the frictional force remains at the maximum possible value.

7 of 15

## Work and Power

work done= energy tranferred

Joules= energy for work

work done= force x distance moved

power= work done/ time taken

8 of 15

## Sankey Diagrams

The thickness of each arrow is proportional to the amount of energy involved at that stage.

Input on the left.

Heat energy(wasted) on the bottom.

Output on the right.

9 of 15

## Density

The units for density are g/cm3.

Density(P-Rho)= mass/ volume

Volume= mass/ density

mass=density x volume

10 of 15

## Pressure

The unit for pressure is the Pascal(Pa). It can also be written as N/m3

Pressure=force/ area

Area= force / area

Force= pressure x area

Pressure between liquids and solids= Pressure= density x gravity x height

11 of 15

## Hydraulics

All hydraulic systems use 2 pistons linked via a pipe carrying a special oil called hydraulic fluid.

Pressure= force applied/ area of master piston

Pressure= force exerted/ area of slave

12 of 15

## Forces

Moment= force x distance from pivot

Moments are measured in Newton metres(Nm)

13 of 15

## Hookes Law

A car would topple if the centre of mass is on the outside of the wheel.

Force= spring constant x extension

L/m=spring constant

14 of 15

## Springs

Newtons=kg's x gravity-10m/s2

15 of 15