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chapter 9 - Coggle Diagram

- - - - Resistance = resistivity*Length of wire / Cross sectional area of wire
      - R, resistance (Ω)
      - ρ (rho), resistivity (Ωm)
      - A, cross sectional Area (m^2)
      - This equation may be used for a known constant temperature as resistivity of a material is affected by temperature
  - - - The resistivity of a material at a given temperature is the product of the resistance of a component made of the material and its cross sectional area, divided by its length.
- - - - It takes energy to push charge through a component, and the higher the resistance of that component, the more energy it takes.
  - - - The ohm is defined as the resistance of a component of 1V is porduce per ampere of current
        
        1Ω = 1 V A^-1
  - - - Basically, when the p.d. is doubles, the current in the wire also doubles
    - - hotter = more resistance
        
        This is because as the temperature increases, the positive ions inside the wire have more internal energy and vibrate with greater amplitude about their postitions
        
        The frequency of collisions between the charge carriers (free electrson in the metal) and the positive ions increase
        
        This means that the charge carriers do more work, i.e. on the wire, and so transfer more energy as they travel through the wire
      - Other factors that affect resistance
        
        material
        
        length of wire L
        
        Resistance ∝ length
        
        cross-sectional area of the wire A
        
        Resistance ∝ 1/A
        
        there fore R ∝ L/A
  - - - In some semiconductors, as the temperature increases, the number density of charge carriers also increases
- - - - power P, (W)
      - energy transferred, W (J)
      - time, t (s)
- - - - These electrons have very precisely determined kinetic energies
- - - - Designed to ensure a constant resistance
        
        The steeper the line, the lower the resistance
      - From the graph we can draw the conclusions that
        
        V ∝ I
        
        resistors obey Ohm's law, so is an ohmic conductor
        
        constant resistance
        
        behaves the same way regardless of polarity
    - - From the graph we can conclude
        
        V is not directly proportional to I
        
        does not obey Ohm's law, is a non-ohmic conductor
        
        not a constant resistance
        
        Behaves the same way regardless of polarity
        
        Resistance increases as the p.d. across it increases
      - The increase in resistance (i.e. the flattening of the graph as time goes on) is caused by the wire getting so hot that it glows
        
        As the current increases so does the rate of flow of charge through the filament, more electrons per second pass through it
        
        this leads to more collision between the electrons and the ions
        
        the electrons transfer energy to the ions when they collide causing ions to vibrate more, and increase in termperatire, and collide with even more electrons
  - - - Uses a variable resistor to provide different values of I
        
        It is important while investigating the I-V characteristic to reverse the polarity of the battery/power supply normally, to look at whether the component behaves in the same way as the other direction.
    - - uses a potentiometer to provide different values of V
  - - - from the graph we can see that
        
        The potential difference across a diode is not directly proportional to the current through it
        
        so therefore does not obey ohm's law and is a non-ohmic component
        
        the resistance of the diode is not constant
        
        the diode's behaviour depends on the polarity
      - At A: the resistance is very high(infinite for practical purposes)
      - At B, as the p.d. increases, the resistance gradually starts to drop
        
        For a silocon diode, this happens at around 0.7V (known as the threshhold p.d.)
        
        the threshold p.d. is different for each LED relating to the colour of light they emit
      - above B, the resitance drops sharply for every small increase in p.d. so very little resistance
  - - - non-ohmic
      - not a straight line so resistance is changing
- - - - In Dark conditions the LDR has a very high resistance
        
        The number of free electrons inside the semiconductor is very low, so the resistance is very high (often into MΩ
      - In light conditions, light shines into an LDR and the number densityy of charge carriers increases dramatically
        
        Leading to a rapid decrease in the resistance of the LDR
  - - - Resistance Y-axis
        
        light intensity (Wm^2) x-axis
  - - - Can even see inside dense clouds of gas and dust with infrared, which passes through these clouds, unlike visible light which does not.
- - - - the term p.d. is used when charged particles lose energy in a component
    - - One volt is the p.d. across a component when 1J of energy is transferred per unit charge passing through the component
      - 1V = 1JC^-1
    - - potential difference or voltage = energy transferred by charge Q / Charge Q
      - V, voltage (V, volts)
      - energy transferred, W (J)
      - Charge, Q (C)
    - - used to measure p.d.
        
        connected in parallel
        
        an ideal voltemeter would have infinite resistance so that when connected, no current passes through the voltmeter itself, but this is not possible in reality
        
        higher resistance is better
  - - - essientially the charges are gaining energy as they pass through components like cell, battery, or power pack etc
    - - electromotive force = energy transferred by charge Q / charge Q
  - - - W = VQ
    - - ℰ = VQ
- - - - Opening a switch or disconnecting a powersource etc the current will fall to zero and no energy will be transferred and the circuit is off
  - - - electrical power P, (W)
      - current, I (A)
      - p.d., V (V)
      - Deriving P=IV
        
        P=W/t
        
        P=VQ/t
        
        P = VI
        
        P=IV
        
        W=VQ
    - - electrical power, P (W)
      - current, I (A)
      - Resistance, R (ohm)
    - - electrical power P, (W)
      - p.d., V (V)
      - Resistance, R (ohm)
  - - - energy transferred, W (J)
      - p.d., V (V)
      - current, I (A)
      - time, t (s)
- - - - In simple thermometers
      - in thermostats to control heating and air-conditioning units
      - to monitor the temperature of components inside electrical devices like computers and smartphones so that they can power down before overheating damages them
      - to measure temperature in a wide variety of electrical devices like toasters, kettles, fridges, freezers, and hair dryers.
      - to monitor engine temperatures to ensure the engine does not overheat
    - - Resistance y-axis
      - temperature x-axis
  - - - Alternatively, instead of an ohmeter, use an ammeter and voltameter and use the equation R = V/I to work out the resistance value.
        
        Results from this experiment may be used in the choice of a thermistor of a particular application for example, an incubator if it operates between 20 and 50 degrees.
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