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Electricity (Capacitors (Energy stored in a capacitor (The amount of…

- - - - When the switch is closed negative charges build up on the plate nearest the negative terminal and these repel the negative charges on the other plate leaving it positively charged.
      - A p.d builds up between the plates and when it is fully charged, the p.d is equal to the source. No more charge flows
      - Current
        
        To begin with her is no charge on the capacitor. The current is limited only by the resistor
        
        As the capacitor charges a p.d develops across the plates. This opposes the p.d of the cell. This results in a current decreas
        
        The capacitor is fully charged and the p.d across the plates is equal and opposite to the cell. No more current flows
      - The circuit starts with the switch open, no charge flowing therefore no charge is stored in the capacitor
    - - The current is flowing in the opposite direction(from negative "peak current" to 0). The discharge current decreases as the p.d across the plates decreases
      - Capacitors store charge but cannot supply more energy (like a battery)
      - Capacitors are however used for the flash in a camera as they release a quick burst of light
    - - Size of capacitor
        
        The bigger the capacitor the longer it takes to charge (both start with the same current)
        
        A larger capacitor will take longer to fill
      - Size of resistor
        
        A big resistor increases the time it takes to charge and affects the size of the current as the start i.e it's smaller
        
        The area under the graph is equal to the charge. Changing the resistor only alters the time it takes to charge. Both areas are the same
  - - - Increasing the voltage of source
      - Increasing the value of the capacitor used
- - - - Biasing the diode
        
        Forward biased diode(e.g. LED)
        
        Electrons from the n-type are given enough energy from the battery to overcome the depletion layer.
        
        They will flow around anticlockwise and the holes flow clockwise
        
        The diode conducts as the depletion layer is removed
        
        Light Emitting Diode
        
        Sometimes biased holes and electrons meet and recombine and the energy is given out as a photon
        
        If light is allowed to escape then an LED is created
        
        The colour depends of the quantity of material
        
        Reverse biased diode
        
        LDR
        
        Connected in reverse bias is known as photo-conductive mode.
        
        When light hits the photodiode (a p-n junction that has transparent coating) the energy will release electrons in the depletion layer to create electron-hole pairs(i.e they will both be free)
        
        This provides a number of free charge carriers in the depletion layer, decreasing resistance and allowing current to flow.
        
        The greater the irradiance, the more free charges and the less resistance
        
        The depletion layer increases, increasing the size of the potential barrier. The diode doesn't conduct
        
        No bias (not connected to a power source). The semiconductor operates in photovoltaic mode.
        
        Photons incident on the junction are absorbed and an electron-hole pair is created
        
        A Voltage is generated by the separation of electron and hole
        
        The more photons, the greater the voltage
        
        To bias a semiconductor means to apply voltage
        
        In a forward biased semiconductor the positive side(n-type) is connected to the positive side of the battery and the negative (p-type) is connected to the negative side of the battery. Reverse biased is opposite this
      - When the a semiconductor is grown with one half p-type and one half n-type we get a p-n junction and it functions as a diode. There will be natural diffusion
      - Diffusion - movement of particles from high concentration to low concentration of the holes and electrons
      - When the holes and electrons combine they leave ions which makes the n-type become positive and the p-type negative.
      - This also creates a potential barrier called the depletion layer and stops current from flowing. To flow, the voltage across the diode must be greater than the potential barrier
- - - - The coulomb
        
        The charges pick up energy as they pass through the power supply and deliver the energy to other parts of the circuit.
        
        1 electron has a negative charge of 1.6 Coulombs
    - - When energy is being provided by an external source the voltage is referred to as electromotive force (e.m.f)
      - When energy is changed from electrical energy to another form in the circuit, the coltage is called a potential difference
      - Energy supplied from the battery is chemical -> electrical. An e.m.f voltage can be measured
      - In a bulb energy is provided by the circuit electrical -> light + heat A p.d (voltage) can be measured
  - - - In a series circuit the voltage across each component is directly proportional to the resistance i.e. the bigger the resistance, the bigger the voltage across it.
      - You can work this out again by using the same method or by using on of the two formulas on the formula sheet
      - Potential Divider - A potential divider is the name we give to a circuit which uses the components to split up the supply voltage (A circuit with two or more "resistors")
        
        Wheatstone Bridge Circuit
        
        A bridge connector is used to join two branches.
        
        The potential difference between points X and Y depends upon the potentials at points X and Y
        
        The potential at Y depends on the ratio of R1 and R2
        
        The potential at Y depends on the ratio of R3 and R4
- - - - Period
        
        The time taken for ONE wave to be produced or pass a point
        
        Measured in seconds
        
        Period can be calculated using T = 1/f
      - Waves are generally produced by something vibrating
      - Frequency is measured in Hertz(Hz)
      - Wavelength is from one point on a wave to the same point on the next wave measured in meters (m)
      - The frequency is the number of waves that are produced or pass a point in one second
      - Frequency = Number of waves / Time
    - - Setting the y gain gives volts per division ( what each box is worth)
      - The time base determines the number of waves seen on a screen
      - The y gain controls the amplitude or height of the waves
      - The setting of the time base gives time per division ( what each box is worth)
      - Peak and r.m.s values
        
        Peak and r.m.s are linked with equations (see formula sheet top of electricity)
        
        Different meters are used to measure current and voltage in AC and DC circuits. In AC circuits they measure the r.m.s voltage (root mean squared)
        
        In any calculation for power, resistance etc we always use the r.m.s values.