Electronics Answerswire line


  1. a) The three system blocks are Input, process and output.
    b) Input = Keyboard.
    Process = microprocessor or CPU
    Output = screen or the VDU.
  2. Picture B is the only digital signal. How can you tell? Simply check that the signal has only two possible values. Pictures A & C have many possible values so they are analogue signals.
  3. Solenoid = electrical to movement. LED = electrical to light. Buzzer = electrical to sound. Relay = electrical to movement.
  4. Use Ohm`s Law. V = I x R.
    In this problem V, the voltage = 6 volts and the resistance = 2k ohms.
    2k means 2,000 ohms.
    So put in the numbers:
    6 = I x 2,000
    So 6 / 2,000 = I
    So I = 0.003A or 3mA
  5. The three voltages are 3V, 4V and 10V. The diagram below shows you how to calculate the output voltage.
    voltage divider
  6. The voltage across it rises to the value of the supply.Check the graph and circuit shown below.
    voltage across capacitor graph
  7. a)When the LDR goes into darkness its resistance increases. As the resistance increases so the voltage across it will increase because it is part of a voltage divider circuit. Remember that in a voltage divider circuit whatever happens to the resistance the voltage will do the same.
    b) As the voltage increases across the LDR tthe voltage across the base and the emitter also increases.
    And if the voltage across the base/emitter of the transistor exceeds 0.7V then the transistor will conduct and the led will light.
    c) The resistor is there to prevent too much current flowing into the base of the transistor.
  8. When switch S1 is closed the voltage across the capacitor increases.
    This voltage appears across the base and emitter of the transistor and if it rises to above 0.7 volts the transistor will switch on. This will let the current through the LED thus making it light.
    By closing switch S2 the capacitor will discharge making the voltage across the base emitter of the transistor fall to 0V. Thus the transistor will switch off therefore no current can flow into the LED, so it goes off.
    This circuit can be used for a timing device that will turn on a light a few seconds after the switch is pressed. This is similar to the push button traffic lights.
  9. This is an OR gate symbol
  10. a) Voltage gain = voltage out / voltage in
    So Voltage gain = 0.5 / 0.5mV
    Voltage gain = 0.5 / 0.0005
    Voltage gain = 1,000

    b) Use the formula P = V2 / R
    Putting in the numbers gives 10 = 0.52 / R
    Rearranging gives 10 x R = 0.25
    So R = 0.25 / 10 = 0.025 ohms


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