Circuits, Waves, Lenses, Heat PDF

-Electricity -- - Electricity is a type of energy caused by charged particles called electrons - As electrons orbit the nucleus, they are not embedded within the atom, allowing them to move from one atom to another - There are two types of electrical energy: - 1. Static --...

-Electricity -- - Electricity is a type of energy caused by charged particles called electrons - As electrons orbit the nucleus, they are not embedded within the atom, allowing them to move from one atom to another - There are two types of electrical energy: - 1. Static -- static as a static electric charge - 2. Dynamic -- moving as a current - When electricity is moving as a current, we can harness the energy by changing the form of the electrical energy Electrical Circuits -- - Electrical circuits are pathways for charged particles (electrons) that direct them to where we want to use their energy. - For an electrical circuit to work it must have three components -- power supply, conductors and a load. - Power Supply -- Source of the electrical charge; where the electrical charge comes from, such as a battery, generator, or a wall outlet - Power Supply -- The power supply also determines the type of current used, AC or DC, the size of the current, and the force behind it - AC -- Alternating Current, in this, the electrical charge (current) changes the direction of its flow periodically - DC -- Direct Current, in this, the electrical charge (current) flows only in one direction -- AC and DC are types of current - Current -- Current is measured in Amperes or Amps (symbol I). One amp is equal to 6.24 x 10 to the 18 electrons passing a point in the circuit every second - Voltage (V) -- The potential energy given to the charges in the power supply. It is the force driving the charge through the circuit and is changed to other forms of energy within the circuit - Conductors -- The pathways for the electrons to travel along. Materials that allow electrons to easily pass through them are called conductors. Conductors create a loop from the power supply to the load and back to the power supply. They must form a complete, closed loop or the electrons will not flow.  - Load -- The load is any component of the circuit that uses the electrical energy. Remember that energy is not destroyed, it just changes form. Examples of a load in a circuit are light bulbs, speakers, and motors. These change electrical energy to light energy, sound energy, and kinetic energy. - Resistance -- It takes energy to push through the conductors and the load. The amount of energy used, or hard it is to push current through a circuit is called resistance and is measured in Ohms (R) Voltage, Amps, and Ohms -- - Voltage (V): the potential energy or change in energy across the circuit, the force used to push current through. - Amps/Amperes (I): how many charged particles move through the circuit. - Ohms (R): the resistance of the circuit (or parts of the circuit), or how hard it is to push the current through. - Factors Affecting Resistance -- - Length - Increasing the length of the conductor increases the resistance - Surface Area/Diameter - Increasing the surface area decreases the resistance - Temperature - Resistance increases with increasing temperature - Material - Different materials have different levels of resistance to current flow Symbols and Circuit Diagrams -- - Circuit diagrams show the setup of an electrical circuit - Diagram -- see slides - Rules for drawing circuits --- - 1. Use pencil - 2. Use a ruler for connecting wires - 3. Make your diagrams large -- 1/4 page minimum - 4. Ensure a complete path in the circuit --- no gaps - Volmetres -- MUST ALWAYS BE CONNECTED IN PARALLEL TO THE COMPONENT YOU ARE MEASURING -- EG A LIGHTBULB - Ammetre -- Gives measurement of current, NEEDS TO BE IN SERIES WITH THE COMPONENT - Resistor -- resists the flow of current in a circuit and use up energy in a circuit by converting it to heat Series and Parallel Circuits -- - When electrons only have a single path to take through multiple components, these components are said to be placed in a series -- one after the other - When electrons have a branch and the current splits to go through multiple different components, these components are said to be in parallel Variables -- - Independent -- Variable that is changed -- X axis - Dependant -- Variable that is affected by the change/independent -- Y axis - Controlled -- Variable that is constant/does not change Ohm's Law -- - This law states that voltage across a conductor is directly proportional to the current flowing through it, provided that all physical conditions and temperature are constant. - If we change the physical conditions -- such as length and material -- we change the resistance -- This has an impact on current - V = IR - Voltage (volts) = Current (Amps/Amperes) x Resistance (Ohms) - It takes 1 volt of force to move to move 1 amp through a resistance of 1 ohm Resistance -- - A measure of how much a material opposes the flow of charge/current through it - Low Resistance = High Current - High Resistance = Low Current - Units is Ohms - R = Ohms - Therefore, Resistance and Current are inversely proportional - HEAT GENERATION-- - Metal conductors are made up of lattice -- repeating structures of positive ions - Electrons -- negative ions -- can move freely -- reason for good conductors - Collisions between electrons and positive ion lattice structure are what cause resistance as the collisions cause vibrations that generate heat - Transfer of electrical energy to heat energy Ohmic vs Non Ohmic Resistors -- - Ohm’s laws states that if all the physical qualities stay the same, there is a directly proportional relationship between voltage and current - Resistors that follow Ohm’s law are called Ohmic Resistors; If you graph current vs voltage for ohmic resistors, you will get a straight line - Note --- for current (amps) vs voltage, current is always Independent variable (X axis) and voltage is always Dependent variable (Y axis) - Some resistors do not follow Ohm’s law and change their resistance with different physical properties such as temperature, voltage, or light - These are called Non Ohmic resistors and when you graph them with current vs voltage, you will get a curved line that has no directly proportional relationship Series Circuits -- - A circuit where all the components are linked in a single loop - Only one path for current to flow through - VOLTAGE -- - All the voltage in the circuit will be used in the components/lights - CURRENT -- - All components will receive the same amount of current due to the single path - Electrons flow at the same rate Parallel Circuits -- - A circuit with a junction where the circuit splits into two or more paths and reconnects later - VOLTAGE -- - The voltage is always the same in each branch of the circuit Total Resistance (Ohms) in Series Circuits -- - In a series circuit, we find the total resistance in a circuit by adding the value of each resistor in the circuit. - Rtotal = R1 + R2 + R3 etc - Rtotal = R1 + R2 + R3 - Rtotal = 3 Ohms + 10 Ohms + 5 Ohms - Rtotal = 18 Ohms Total Voltage (V) in Series Circuits -- - The voltage across any single component in a circuit can be determined using V=IR - The voltage across a complete series circuit can be determined using V=IRTotal - The sum of the voltages across all resistances is equal to the voltage applied by the power source. Voltage can be different at different points in the circuit! - VTotal = V1 + V2 + V3 etc Total Current (Amps) in Series Circuits -- - The total current in a series circuit is found using V=IRTotal - The current in a series circuit is the same at every point in the circuit! Total Resistance (Ohms) in Parallel Circuits -- - In parallel circuits, where electrons have multiple paths, the total resistance is the inverse of the sum of the resistance across each pathway. - 1/RTotal = 1/R1 + 1/R2 + 1/R3 etc Total Voltage (V) in Parallel Circuits -- - The voltage used across every branch of a PARALLEL circuit is the same, and is the same as the voltage from the power source. - Across any single component voltage can be found using V=IR Total Current (Amps) in a Parallel Circuit -- - The SUM of the current in all the branches of a parallel circuit is equal to the current pushed out of the power sources. Graphing -- - LUST --- - Labels - Units - Scale/Spacing - Title - Use X’s - Draw a line of best fit - Do not add zero unless explicitly stated or in the results of the experiment V = IR TRIANGLE-- - V = IR --- Voltage = Current (Amps) x Resistance (Ohms) - I = V/R --- Current (Amps) = Voltage/Resistance (Ohms) - R = V/I --- Resistance (Ohms) = Voltage/Current (Amps) NOTE -- 1000 mA (Milliamperes) = 1 Amp Validity and Reliability -- - Validity -- refers to how accurately a method measures what it is intended to measure. - To ensure our experiment is valid, we must make sure we are using the correct equipment, in the correct way. Controls are important to ensure that changes measured in your dependent variable are only due to changes in the independent variable. Controls improve validity. - Reliability is how many times you repeat the experiment and come to similar results. - Reliability is how many times you repeat the experiment and come to similar results. If time permits, repeat the experiment and compare the data. Law of Conservation of Energy / Energy Transformations -- - The purpose of electrical devices is to transform electrical energy into other, useful forms as energy cannot be created or destroyed, only changed in form. - In an electrical circuit the load is what converts the energy into another form. - Examples are resistors, light bulbs, speakers and motors. These transform electrical energy into heat, light, sound and kinetic energy respectively. Current -- - Electrical current is the rate of flow of charge in a circuit - An object that contains charged particles and can makes these particles flow with the use of an energy source like a power supply/battery as it gives the charges the energy to move - As the charges move around, the can transfer their energy to components like lightbulbs - Current is responsible for electrical energy transfer around a circuit - In current, only electrons move - Conventional current goes in the opposite direction to the electrons in a circuit - Conventional current is positive charge to negative - Voltage and Electrical Potential Energy -- - Electrical potential energy is the measure of the energy that is available to each charge in a circuit - Potential difference is the difference in energy in two points in a circuit - The greater the potential difference, the greater the energy - Unless there is a potential difference in a circuit, the current will not flow - Conventional current will always flow from a point of high potential to low potential Energy stored in an object due to its position is Potential Energy. Energy that a moving object has due to its motion is Kinetic Energy. WAVES -- - Waves are vibrations or oscillations that move energy from one place to another - The rest position is called the equilibrium position and something physical must be oscillating -- moving back and forth -- around this position - Only energy is being transferred not matter - The wave itself moves from place to place but the matter it moves through only oscillates around the same position Transverse Waves -- - The particles in the medium vibrate perpendicular to the direction the wave moves - The trough of a wave is the point on the medium that exhibits the maximum amount of negative or downward displacement from the rest position. - An example of this are electromagnetic waves and water waves - The crest of a wave is the point on the medium that exhibits the maximum amount of positive or upward displacement from the rest position. - The amplitude of a wave refers to the maximum amount of displacement of a particle on the medium from its rest position. - The wavelength of a wave is simply the length of one complete wave cycle. Longitudinal Waves -- - The particles in the medium vibrate parallel to the direction the wave moves - An example of this are sound waves, springs, and seismic waves from earthquakes - Compression:region of high pressure and high particle density in the wave. Increased pressure causes particles of the medium to be pushed closer together, either by a source of vibration or by the preceding rarefaction. - Rarefaction: region of low pressure and low particle density in the wave. It occurs when the particles of the medium are spread farther apart than their equilibrium positions. Wave Features -- Amplitude -- - The maximum displacement/distance of a point on a wave away from the equilibrium ie the crest and trough Wavelength -- - The distance from a point on one wave to the equivalent point on the next/adjacent wave - The distance between 2 peaks - Amplitude and wavelength describe distances Frequency -- - The number of points passing a particular point every second - This is measured in Hertz - Frequency = 1/period Period -- - The amount of time it takes for a wave to pass a particular point - Inverse of frequency Speed -- - The distance travelled by each wave per second - FORMULA - Speed = Frequency x Wavelength - Distance of waves always measured in metres per second LENSES -- - A transparent material that light can pass through - They use refraction to bend and distort the images seen through them Convex Lens -- - Horizontal line pass through the principal focus and converge - Converging lenses Concave Lens -- - Rays passing through the lens will diverge from this point - Diverging lenses Focal Length -- - How far the focus is from the centre of the lens - Lens with small focal lengths are more powerful as they have to bend the light more - The more rounded the lens is, the more powerful the lens will be as the light will bend more Ray Diagrams -- - Tracking the paths of light travelling from an object through our lens - Used to estimate the effect the lens will have on the light passing through, and tell us about the image formed in the lens HEAT TRANSFER -- Conduction -- - When particles collide with each other to transfer thermal energy or heat from a hotter region to a colder region - Heat will always move from hot to cold - The particles in a hotter substance have higher kinetic energy than that of a colder substance - Therefore the particles in the hotter region have more energy and movie faster - As the high energy particles collide with the low energy particles, the transfer energy - This will continue until all particles are the same temperature -- this is called thermal equilibrium - Bad thermal conductors are called thermal insulators -- nonmetals, liquids, gases Convection -- - Mainly for fluids - When a fluid is heated up and moves away from its heat source, carrying thermal energy away, and forcing colder parts of the fluid closer to the heat source - Convection current -- works for liquids and gases - Transfer of energy as fluid particles move from hotter to colder regions Radiation -- - When an object emits electromagnetic waves, which carry away thermal energy that can be used to heat up another object, transferring the energy. - Does not need contact between a hot and cold region to transfer energy - Does not need a medium to travel through as it uses electromagnetic waves