Potential Difference, Current and Resistance Voltage Current Resistance How to Measure Voltage, Current and Resistance

Potential Energy Potential Energy = the energy stored in an object Every electron has potential energy Potential Energy = the energy stored in an object Every electron has potential energy Apple tree example Apple tree - two apples in a tree, one high and one low both appes have energy stored in them when the appe falls is converts its sotred energy into potential energy, into motion Which Apple has the greatest potential energy and why? Apple in a higher branch (more energy to convert, longer way to fall)

Potential Difference Potential Difference or Voltage (V) = The source of energy in a circuit provides energy to the electrons. Voltage is described as the force that moves electric charges in a circuit. It is how much energy that the electrons pick up from the source. igher the potential difference (voltage) the greater the potential energy of each electron PD – another words = voltage A battery had potential energy in the electrolyte of its electrochemical cells The chemical in the electrolyte react with the electrode that causes a difference in the amount of electrons between the two terminals One end has a negative charge (electrons) and the other end had the positive charge The ngative electrons are attrached to the positive end of the battery and move toward it throught the use of a conductor (ie copper wire) like falling apple from a tree PD – causes current to flow in a closed circuit

Measuring Potential Difference Volt (V) – is the unit used to measure potential difference Voltmeter Measures the potential difference between two locations in a circuit A voltmeter is connected in parallel What is the apparatus used to measure potential difference? Placing the two end of the voltmeter and measure the potential differnece in a battery

Electrical Current Electrical Current = is the number and speed of the electrons that are moving through the circuit. Think of the continuous flow of electric current like water flowing in a stream The water keeps flowing unless the source dries up As long as the battery continues to separate charges on its terminals (ends) the electrons will continue to flow WB – example of DC WB – example of alternating current

Measuring Current The electric current is measured in units called – Ampere (A) The symbol for current is I Ammeter- measures current in a circuit. An ammeter is connected is series. Current Energy moving past a point in the circuit every second

Resistance Conductors have low resistance values Electrons are very small particles. They move very quickly through a circuit but can sometimes be slowed by larger objects that get in their way (like the nuclei of atoms). The ability to slow the movement of electrons in a circuit is called Resistance. ALL SUBSTANCES RESIST ELECTRON FLOW Conductors have low resistance values Insulators have high resistance values When a substance resists the flow of electrons, it slows down the current and converts the electrical energy into other forms of energy The more resistance a substance has they more energy is gains from electrons that pass through it The energy gains by the substance is radiated to its surroundings as heat and/or light energy The more resistance a component has the smaller the conductivity

Conductors and have very little resistance. Insulators have high resistance values. The loads in a circuit tend to have high resistance, to slow the electrons and convert the energy into a useable form of energy. A Light Bulb Filament has a high resistance. - the current in a circuit passes thorugh the light bulb filament The filament is a resistor, slows current flow Converts the current into energy, heat up and produce light WB other examples of resistance

Resistors Resistors can be used to control current or potential difference in a circuit The amount of resistance in a circuit affects the electrical current Current decreases if you add resistance Q: Another word fro potential differences In a circuit electrons have a higher potential difference as tery enter a resistor compared to when they leave the resistor because they use up some energy passing through the resistor Electrons enetering the resistorhave high potential energy electrons exiting the resistor haave had their potential energy converted into another form of energy Like the water flowing in a pipe Thin pipe has more resistence = less flow Thick pip has less resistance = more low

Factors Affecting Resistance Table 11.1: Page. 443 Factor How Factor Affects Resistance Material The material used in a circuit effects the resistance on the circuit Copper is used most frequently as conducting wire Temperature High temperatures have a higher resistance Low temperatures have a lower resistance Length Longer wires have more resistance Shorter wires have less resistance Cross-sectional Area Wide wires have less resistance Short wires have more resistance

Measuring Resistance Ohm (Ω) – the unit used to measure resistance The symbol for resistance is R Ohmmeter Measures electrical resistance Multimeter = measures differnece, current, or resistance Ohm – greek leter omega

Homework Questions 1-3 pg. 442 Questions 2,3,4,5,7,8,10 pg.447