GCSE physics

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Author:
ghoran
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172942
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GCSE physics
Updated:
2012-09-24 16:43:49
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Unit two part three currents electrical circuits four
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revision
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  1. current potential difference graphs are used to 
    show how the curren through a component varies with the p.d. across it
  2. what does the current potential difference graph look like for a resistor (metal wire) at constant temperature
    • straight line through the origin , the current is directly proportional to the voltage
  3. how do we use a currrent potential differnce graph to find the resistance 
    • the gradient = p.d./current 
    • the gradient = resistance 
  4. what can we conclude from a current potential difference graph for a resistor (metal wire) at constant temperature 
    OHMS LAW - the current through a resistor (at constant temperature)is directly proportional to the p.d. across the resistor 
  5. A) what is the conclusion to an experiment to investigate the relation between the p.d. across a filament lamp and the current through it
    B) what differences have you found when the component is allowed to get hot 
    • A) the resistance of a filament bulb increases as the temperature of the filament increases
    •  b) as the current increases it heats the filament and the resistance increases
  6. what is the graph for an experiment to investigate the relation between the p.d. across a filament lamp and the current through it
  7. what is a dioide
    • it is a component that allows current through itself in one directiom but not the other 
    • diodes convert alternating current into direct current
  8. this graph shows that as the current increases , the resistance of the filament
    increases because as the current increases it heats the wire and the resistance increases
  9. Faced with the arrow head pointing to the right the diode has a ........ Resistance . A ....... .... and the bulb ....... Light up . We say the diode is ..... .....
    • Low 
    • cureent flows 
    • does 
    • forward biased
  10. faced with the arrow head pointing to the left the diode has a very ...... Resistance . . .... ..... Flows so the bulb ..... Light up . We say the diode is ..... ....
    • High 
    • no current 
    • doesnt 
    • reversed biased 
  11. The current through a diode flows 
    In one direction only . The diode has a very large resistance in the reverse direction 
  12. What is the graph for an experiment to investigate the relation between the p.d. Across a diode and the current through it
  13. For our experiment with the resistor and the filament lamp we plotted voltage on the y axis and current on the x axis . This meant that the gradient of the graph was voltage/current I.e. resistance . For the diode it is tradional to 
    • Plot the current on the y axis and voltage on the x axis and to show both + and - values on the graph 
    • you may still use reasistance = voltage/current but the gradient does not equal the resistance 
  14. What does LED stand for 
    Light emitting diode 
  15. An LED emits light when 
    A current flows through it in the forward direction
  16. There is an increasing use of LED's for lighting because they
    Use a much smaller current than other forms of lighting
  17. What does LDR stand for 
    light dependant resistor 
  18. the resistance of A LDR decreases as 
    The light intensity increases 
  19. When you cover the LDR the light intensity
    Decreases the resistance increases and the current decreases . The opposite happens when you uncover the LDR
  20. what are the uses of an LDR 
    • Photographers light meter 
    • burglary alarms
    • automagic hand drier  
  21. The resistance of a thermistor decreases as the 
    Temperature increases 
  22. When you heat a thermistor the 
    Resistance decreases and the current increases 
  23. What are the uses of a thermistor
    • Electronic thermometer
    • fire alarm 
  24. Name the comment of each phrase 
    a) it's resistance decreases as it gets hotter 
    b) it's resistance increases as it gets hotter 
    c) it's resistance depends on which way it is connected in a circuit
    d) it's resistance increasget when you cover it 
    • A) thermistor 
    • b) lamp 
    • c) diode 
    • d) LDR 
  25. What ippt he graph to show how the resistance of a thermistor changes with current
  26. State and explain how the current in a curcuit with a thermistor connected in a series with a cell and resistor changes when the temperature of the thermistor increases 
    As it gets hotter it frees more electrons to increase the current 
  27. A LDR connected in a series with a resistor , and ammeter and a battery . A voltmeter is connected across the resistor . Explain why the ammeter reading decreases when the LDR In daylight is covered
    Because when  it is covered there is less light and  the resistance increases and the current decreases
  28. For compnents connected in series 
    • The total resistance is the sum of the resistance of each component
    • there is the same current through each component 
    • the p.d. Of the supply is shared between the components 
  29. A

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