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Kelso High School S2 Electricity and Light Summary Notes Name ………………………………………………………….. Class ……………………….. Electricity Circuit symbols are used to draw electric circuit diagrams. name of component name of component symbol Cell / battery switch wire voltmeter lamp fuse resistor ammeter variable resistor motor You should be able to draw simple circuit diagrams following the rules symbol V A M Always use a pencil and ruler Make wires straight with right angles Make sure wires touch components Never draw components at the corners Electric current flows through the wires in a circuit when there are no gaps in it. An electric current is a flow of small particles called electrons (similar to water flowing through a pipe). They are negatively charged so go from the negative terminal to the positive terminal Electrons carry energy around a circuit. A series circuit has only one path for the current to take. A parallel circuit has more than one path for the current to take. 1 4 An ammeter measures the size of a current in Amps (A). An ammeter is connected in series in a circuit. The current in a series circuit is the same at all points A2 3 I1 = I2 = I3 = I4 AT The current in the branches of a parallel circuit add up to the total current IT = I1 + I2 + I3 A1 A2 A3 A battery gives energy to the electron and ‘pushes’ it around a circuit. A voltmeter measures the size of the ‘push’ in volts (V). A voltmeter is placed in parallel across a component to measure voltage. V supply V 1 V 2 The voltage in a series circuit adds up to the voltage of the supply supply 1 Vs = V1 + V2 2 The voltage in a parallel circuit is the same across each component. 3 Vs = V1 = V2 = V3 You should be able to work out the current at different parts of a circuit. Put your finger at the negative side of the battery and trace the route through the bulb and motor. There is only one path so all the current goes through the bulb and the motor. The route then splits into two , If the resistors are the same strength half the current will go each way. The current joins together again so the current at position 3 is the same as through the bulb. 3 1 M 2 Current Current Current Current Current through bulb = 6A through motor = 6A through resistor 1 = 3A through resistor 2 = 3A at position 3 = 6A Light The law of reflection The angle of incidence equals the angle of reflection Normal Angle of incidence Angle of reflection Mirror You should know some uses for reflection Car head light Periscope Endoscopes use total internal reflection Refraction is when waves change speed due to travelling in a different medium. You should be able to draw these ray diagrams Concave lens Convex lens You should know some uses of refraction. glasses camera microscope telescope binoculars You should be able to label these parts of the eye. Retina Iris Optic nerve Pupil Cornea Lens Cillary muscles Blind spot The pupil lets light into your eye. When it is dark your pupil is large to let in more light. When it is bright your pupil is small so that too much light doesn’t get in. Pupils size in the dark Pupils size in the light The lens focuses light on the back of your eye. A thin lens bends light less than a fat lens. The shape of your lens changes to allow you to see near and far objects sharply The retina picks up the light that lands on it and sends a message to your brain. The blind spot is the one place on the back of your eye where there is no retina so the picture is not seen Your eyes and brain can be tricked. Optical illusions can fool you, so it’s a good idea to always measure things and not just rely on looking at them Different colours of light refract by different amounts. Write how you could remember the order here. White light Refracted least Red Orange Yellow Green Blue Indigo Violet. Refracted most Glass prism Colour addition of light. cyan Blue magenta white red green yellow Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding red and green makes yellow Adding red, blue and green makes white. Test Yourself Questions Electricity 1. For each of the photographs draw a circuit diagram. (a) (b) switch motor bulb Bulb switch fuse Bulb 2. Which of the above circuits shows a series circuit? 3. Do electrons have a negative or positive charge? 4. (a) Draw a series circuit using 2 batteries, a bulb and a motor. (b) Put an arrow on your circuit to show the direction the current flows in. (c) Add a voltmeter across the motor. (d) If the current through the bulb is 2A what is the current through the motor? (e) If the voltage across the motor is 3V and across the bulb is 2V. What is the supply voltage? 5. Do the electricity quiz you will find in the learning resources. Test Yourself Questions Light 1. State the law of reflection. 2. Name at least 2 things that use reflection. 3. What always changes when light goes from air into glass? 4. Draw a ray diagram for a concave lens. 5. Name at least 3 things that use refraction. 6. What does the pupil in your eye do? 7. Which part of your eye detects the light? 8. Will a thin or thick lens bend light the most? 9. List the colours of a rain bow starting with the one that refracts the most. 10.What 3 colours are needed to make white light? 11. Which 2 colours make yellow light? Answers Electricity 1. (a) (b) M 2. (b) 3. negative 3. 4. (d) 2 A (e) 5 V M V Answers Light 1. The incident angle equals the refracted angle 2. Mirrors, periscopes, torches, endoscopes, car head lights and many more. 3. Speed 4. 5. glasses, camera, telescope, microscope, binoculars and many more. 6. Lets light into your eye. 7. Retina 8. Thick 9. Violet, indigo, blue, green, yellow, orange, red. 10. Red, blue, green 11. Red and green.