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Transcript
Loadall Challenge Electricity and Switches This week you will be: • Learning about electricity and the definitions of Voltage, Current and Resistance • Learning about soldering, wiring and how to connect a switch • Building you Loadall’s electrical circuit Electronics • Electronics allow you to control things very precisely • In this project you will use electronics to move the boom arm backwards and forwards • There are three main things we measure in electric circuits: • Current (I) • Voltage (V) • Resistance (R) Resistance (R) Restricts flow of current Voltage Pushes current around circuit Current (I) Flows around the circuit Current (I) • Current is a measure of how many charged particles (called electrons) are flowing along a wire. • The more electrons, the more current flowing. • You can imagine the wire as a pipe and the current as the amount of water that flows along the pipe. • Amperes (A), known as “Amps” for short, are used to measure current. More Current More water flowing through the pipe. Less Current Less water flowing through the pipe. Voltage (V) • Voltage is a measure of the difference in charge between two points on the circuit The diagram below shows how water pressure in a pipe is like voltage in a battery • Voltage tells you how much the charged particles (electrons) are being pushed around the circuit • Voltage is a bit like the pressure in a pipe. The higher the pressure, the more the water is being pushed around the pipe • Voltage is measured in Volts (V) More Voltage Water in the pipe is being ‘pushed’ more by the water above. Less Voltage Water in the pipe is being ‘pushed’ less by the water above. Resistance (R) • Resistance is a measure of how difficult it is for current to flow. • The harder it is for the current to flow the greater the resistance. • You can imagine resistance like a pipe that becomes smaller. The smaller pipe makes it harder for water to flow through it. • Resistance is measured in Ohms (Ω). • Components called resistors can be used in circuits to reduce the amount of current flowing. More Resistance Harder for water to flow Less Resistance Easier for water to flow Resistors Can be used in circuits to reduce current flow Ohm’s Law These electrical variables are linked by Ohm’s Law. • Ohm’s Law: 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 = 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 × 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 • Which is often written as: 𝑉 = 𝐼 × 𝑅 • This can be rearranged to show it in terms of current: 𝐼 = • Or in terms of resistance: 𝑅 = 𝑉 𝐼 𝑉 𝑅 Circuits • Below is a simple circuit diagram for a motor. The battery provides power, the motor rotates and can be turned on/off by the switch • For the Loadall project we want to be able to change the direction of the motor so that the boom arm can extend and retract • To reverse the direction that the motor spins in, you simply Battery wire theBattery battery the other way around. wired the other way round Switch M M Motor spinning clockwise Motor spinning anticlockwise Switches • The Loadall project uses a special switch that has three positions: • Extending (motor spinning in one direction) • Retracting (motor spinning in the other direction) • Off • When you press the switch two wires in the circuit change position • Pressing this switch reverses the way the battery is wired. This changes which way the motor spins. Two wires move when switch is pressed Special switch This three-way switch is known as a doublethrow double-pole switch. Position 1 (e.g. Extending) Position 2 (e.g. Retracting) Switch positions Each of the three switch states are shown below Position 1 (e.g. Extending) Off Position 2 (e.g. Retracting) Questions 1) Find the voltage (V) of a circuit with a current (I) of 0.06 amps and a 200 ohm resistor (R). 2) A circuit consists of a 12V battery connected across a single resistor. If the current in the circuit is 3A, calculate the size of the resistor. 3) A circuit has a 12 ohm resistor and a 24 volt battery. Find the current. 4) Find the resistance of a circuit that draws 0.2 amperes through two 6 volt batteries. 5) A circuit with a 10Ω resistor has 0.9A current flowing through it. Find the voltage of the battery. 6) The resistor in the same circuit is changed to a 50Ω resistor. What is the current of the circuit now? Answers 1) 12 V V = I × R = 0.06 × 200 = 12 V 2) 4 Ω R = V ÷ I = 12 ÷ 3 = 4 Ω 3) 2 A I = V × R= 24 × 12 = 2 A 4) 60 Ω R = V ÷ I = (2 × 6) ÷ 0.2 = 12 ÷ 0.2 = 60 Ω 5) 9 V V = I × R = 0.9 × 10 = 9 V 6) 0.09 A I = V ÷ R = 9 ÷ 50 = 0.18 A The circuit diagram used in this project Soldering a Circuit Soldering can be used to connect wires when creating your circuit: 1) First put the soldering iron in it’s stand and wait for it to heat up 2) While waiting cut the wires to length and strip the ends so that bare metal is showing 3) Then position the bare wire against the terminal you want to join it to 4) Next place the tip of the soldering iron against this point to heat up the wire and the terminal 5) Using your free hand, feed the end of the solder onto the connection point and wait for it to melt 6) Once the solder has melted remove the solder, and then the soldering iron. 7) Hold the wire steady until the solder cools. Recap • Voltage, current and resistance are the key things we measure in circuits • They are linked by Ohms Law: 𝑉 = 𝐼×𝑅 • By wiring a motor the other way round you can change which way round it spins • The STEM project uses a special type of switch (double-pole, double-throw) so that you can change which way round the motor is wired • This means you can make the motor spin clockwise or anti- Resistance (R) Restricts flow of current Voltage Pushes current around circuit Current (I) Flows around the circuit Practical – Wiring the Circuit Use soldering to connect the wires to the switch 1) Connect a red wire (positive power) between two opposite corners of the switch (as shown) 2) Connect a black wire to the other two corners of the switch 3) Use a longer red wire to connect the battery to the first switch terminal 4) Use a long black wire to connect the other side of the battery to the second switch terminal 5) Connect two blue wires from the motor to the two middle terminals of the switch Switch wiring diagram. Each of the points 1-6 is called a ‘terminal’