PHYSICS NOTES

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acts on the Clockwise direction and the other in the opposite, Anti-clockwise direction When a system is equilibrium (balanced) we can say that the clockwise moment must equal the anti- clockwise moment about the pivot meshed area Pulleys 1. Single pulley Anticlockwise Load 3 N Effort Force When teeth come in contact they meshed Three or more gears are called a gear train Gears turn on an axle, similar to a wheel Many different gears designed for different purposes Lesson 4-Pulleys F teeth Load 3N 2. Two single pulleys 0.8 m axle Gears Gears can be used to transfer forces and motion from one object to another. Some gear systems can also be used to change the speed and direction of the motion Gears have teeth on them that interlock with teeth from other gears Effort Force 1.8 m Pivot Force x distance (clockwise) = force x distance (anticlockwise) 3. A single and double pulley Load 2N Clockwise 40 N Effort force Helical Gear Worm Gears [ 4. Two double pulleys Load N ACWM CWM Fx 0.840 x 1.8 Effort Force Fx 0.8 = 72 F F = 72/0.8 = 90N Spur Gear Beuel Gear Rack & Pinion Gear Sprockets Gear Increasing the amount of ropes reduces the effort needed More pulleys and rope causes friction The rope number = ratio The effort has to move much further to lift the load the same distance A pulley system is a force multiplier, by increasing the number of ropes which support the load One rope but three parallel pieces means each part lifts 1/3 Load = ropes x effort Effort = load / ropes Energy cannot be created or destroyed, simply changed from one form to another The load cannot gain more potential energy than the man provides by doing work on it, even if he pulls more rope through his hands This is because he using LESS force Principles of Electricity Current measures the number of electrons through a wire per second The bigger the wire the more electrons there are in it so more can flow through it Current is measured in amperes, or Amps (A) Voltage measures the amount of pressure pushing electrons through a wire, like pressure of water in a hose The more the voltage is increased, the more energy os available to move electrons through Voltage is measured in volts (V) Power measures the rate of work done by electricity. The higher the voltage and current the more electric power available in the circuit Power is measured in watts (W) Symbol Electricity is the effect of stationary or moving charges; like lightening Clouds store charge and a voltage builds up between the ground and the clouds, a lightening strike occurs when the potential difference (voltage) reaches about 10 million volts Current of up to 200,00 amps and 500 million joules can happen Enough energy to power a 100-watt bulb for + T. A Label Cell The energy transferred = the work done = force x distance Battery Resistor Voltmete Ammeter LED Symbol # Label Electricity Diode Switch open Switch closed LDR VARIABLE RESISTOR Revision Fill in the gaps! Symbol & F THE + Bulb Cell Battery Resistor Variable Resistor Diode Light Emitting Diode LED Dependent Resistor LOR Changes electrical ene into light energy Provides energy for the circuit. Stores electric charge. A component which limits the amount of cument na circuit Changes resistance of the circuit. Allows current to flow Allows current to flow in one direction only and gives out light. The resistance changes when the light level changes Bright-Low resistance Dark Highresistance around 2 months Conductors and insulators Conductors are materials which allow electrical current to flow Dust to a large amount of free electrons which act as the charge carries and can move more freely Insulators are materials which d not allow electrical current to flow due to not having many free electrons. 5 electrical conductors Silver Gold Copper Steel Sea water 5 electrical insulators - Rubber Glass Oil - Diamond Dry wood Current Electricity The electrons which flow carry an electric charge, they are described as having a NEGATIVE charge Electric current is defined as the rate f flow of charge I=Q/T A flash of lightning carries 10C of charge and flows for 0.01s. What is the current 1 =q/t = 10C / 0.01s = 1000 A Series circuit Advantage - if the switch is pressed the circuit goes out Disadvantage - when one component breaks the other break Current stays the same in a series circuit The current is the same everywhere and can be calculated by dividing the voltage by the total circuit resistance Parallel circuit The current in parallel circuits split at a junction If two or more components in parallel have the same resistance the current will split equally Current splits in a parallel circuit Fig.2.2 ܢܩ ܩ ܩ Formed when two or more components are connected so the current can flow through one without having to flow through another component first Ammeters and voltmeter Ammeters are connected in series in a circuit as they have negligible (unimportant) resistance and will not have any effect on the circuit. Voltmeters are connected in parallel in a circuit in order to minimise the effect on the circuit as they have a very high resistance resistance makes it harder for current to flow in circuit and affects the size of the current Voltage in series The voltage os the supply (battery or mains) splits between components The split is proportional to their resistance If three composers in series have equal resistance the voltage will split evenly Voltage in parallel The voltage across all branches in a parallel circuit is the same as the voltage of the supply (battery or mains) Resistance and Ohm's Law Resistance = voltage / current 3A More components in series increase resistance More components in parallel decrease resistance A Ammeter in series V₁ = 4V 1A 1A 1A Cell, battery or power supply Load (resistor, bulb, motor or heater) Voltmeter in parallel V V₂ = 12 V V₂ = 4 V 1.5V 1.5V 1.5V 0 1.5V V₁ = 4 V Resistance is measured in Ohm's (22) This means the resistance is the number of volts required to push each amp through a component