P2.3.1 – Static Electricity. Objectives, to understand that: –When certain electrical insulators are rubbed together they become electrically charged.

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  • Slide 1
  • P2.3.1 Static Electricity
  • Slide 2
  • Objectives, to understand that: When certain electrical insulators are rubbed together they become electrically charged. Objects can become charged when electrons are transferred from one to another. Similarly charged objects repel one another. Electrical Charges
  • Slide 3
  • Explain how a charged rod can attract a neutral piece of paper. How large a piece of paper can you pick up?
  • Slide 4
  • Explain how a charged rod can attract a neutral piece of paper. How large a piece of paper can you pick up?
  • Slide 5
  • When certain insulating materials are rubbed against each other they become electrically charged. Negatively charged electrons are rubbed off one material and onto the other. The material that gains electrons becomes negatively charged. The material that loses electrons is left with an equal positive charge. When two electrically charged objects are brought together they exert a force on each other.
  • Slide 6
  • What is electric current? What is current measured in? What is the difference between a series and parallel circuit? How many circuit symbols can you draw?
  • Slide 7
  • P2.3.2 Electric Circuits
  • Slide 8
  • By the end of today: You should be able to draw circuit symbols for common components. Describe what these things actually do. Some will be able to use these symbols to draw circuit diagrams. Electric Circuits
  • Slide 9
  • Can you light a bulb with just one wire?
  • Slide 10
  • By the end of today: You will know where to put an ammeter and a voltmeter in a circuit. You will be able to describe how to measure the resistance of a component. You can state Ohms law. Some will be able to rearrange the resistance equation. Resistance
  • Slide 11
  • Ohms Law The current through a resistor at a constant temperature is directly proportional to the potential difference across the resistor. This means if you double the current you double the voltage over a component. It also means that the resistance of the component does not change when you put more current through it.
  • Slide 12
  • Starter How many different circuits can you draw with 3 cells and 4 bulbs? 10?
  • Slide 13
  • Series and Parallel Circuits
  • Slide 14
  • Series Circuit The components in the circuit are lined up in series, one after each other.
  • Slide 15
  • Parallel Circuit The components in the circuit are lined up in parallel, in parallel lines to one another.
  • Slide 16
  • Series Circuit The current (electrons) can only go one way so the current is the same everywhere in the circuit. But the energy it has given to it by the battery is shared equally amongst all the bulbs.
  • Slide 17
  • Parallel Circuit The components in the circuit are lined up in parallel, in parallel lines to one another.
  • Slide 18
  • Resistance of Components
  • Slide 19
  • By the end of today: You should be able to recognise the graph of current against voltage for a diode, filament lamp, thermistor and LDR 5.3 Resistance of Components
  • Slide 20
  • AV An ammeter measures the current in the circuit A voltmeter measures the potential difference across a component.
  • Slide 21
  • AV
  • Slide 22
  • AV bit of wire http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc How to measure resistance
  • Slide 23
  • Current (A) Potential Difference (Volts) Current (A) Potential Difference (Volts)
  • Slide 24
  • Current (A) Potential Difference (Volts) R = V I If the gradient is constant then the ratio of V to I is constant. so the resistance is constant A Resistor
  • Slide 25
  • A Filament Lamp The filament lamp is a common type of light bulb. It contains a thin coil of wire called the filament. This heats up when an electric current passes through it, and produces light as a result.
  • Slide 26
  • A Filament Lamp The filament lamp does not follow Ohms Law. Its resistance increases as the temperature of its filament increases. So the current flowing through a filament lamp is not directly proportional to the voltage across it. This is the graph of current against voltage for a filament lamp.
  • Slide 27
  • The diode
  • Slide 28
  • If the diode is this way round, no current can flow so the lamp stays unlit.
  • Slide 29
  • The diode has a very high resistance in one direction. This means that current can only flow in the other direction. This is the graph of current against potential difference for a diode.
  • Slide 30
  • Conventional Current A By scientific convention the current goes from the positive end of the battery to the negative end.
  • Slide 31
  • Conventional Current A But current in an electronic circuit is the flow of electrons. Electrons are negatively charged. So the electrons actually go the other way around the circuit to what conventional current says.
  • Slide 32
  • What is negative current and voltage? A Consider conventional current (+ve to ve) +ve reading
  • Slide 33
  • What is negative current and voltage? A If we turn the battery around we send the current the other way around the circuit, this gives us a negative reading on the ammeter. -ve reading
  • Slide 34
  • Thermistors Thermistors are used as temperature sensors - for example, in fire alarms. Their resistance decreases as the temperature increases: At low temperatures, the resistance of a thermistor is high and little current can flow through them. At high temperatures, the resistance of a thermistor is low and more current can flow through them.
  • Slide 35
  • Light Dependent Resistor LDRs are used to detect light levels, for example, in automatic security lights. Their resistance decreases as the light intensity increases: In the dark and at low light levels, the resistance of an LDR is high and little current can flow through it. In bright light, the resistance of an LDR is low and more current can flow through it.
  • Slide 36
  • Extension Tasks Collect your equipment from my desk. Can you set up the multimeter to find the resistance of a component? Draw a superb, artistic, clear diagram of what you have just done. Measure the resistance of a thermistor and an LDR. How can you change their resistance? Does that agree with what you have written in your notes?
  • Slide 37
  • The total resistance (known as R T ) of a series circuit is equal to the sum of the resistance of each individual component. R T = R 1 +R 2 R1R1 R2R2 Resistance of a Circuit

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