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# Introduction To Capacitance

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olhnisnhsohn

olhnisnhsohn

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• Construction and charging and discharging
• ### Transcript

• 1.
• Capacitors
• 2. What is a capacitor?
• Electronic component
• Two conducting surfaces separated by an insulating material
• Stores charge
• Uses
• Time delays
• Filters
• Tuned circuits
• 3. Capacitor construction
• Two metal plates
• Separated by insulating material
• ‘ Sandwich’ construction
• ‘ Swiss roll’ structure
• Capacitance set by...
• 4. Defining capacitance
• ‘ Good’ capacitors store a lot of charge…
• … when only a small voltage is applied
• Capacitance is charge stored per volt
• Capacitance is measured in farads F
• Big unit so nF, mF and  F are used
• 5. Graphical representation
• Equating to the equation of a straight line
Gradient term is the capacitance of the capacitor Charge stored is directly proportional to the applied voltage Q V
• 6. Energy stored by a capacitor
• By general definition E=QV
• product of charge and voltage
• By graphical consideration...
Area term is the energy stored in the capacitor Q V
• 7. Other expressions for energy
• By substitution of Q=CV
• 8. Charging a capacitor
• Current flow
• Initially
• High
• Finally
• Zero
• Exponential model
• Charging factors
• Capacitance
• Resistance
I t
• 9. Discharging a capacitor
• Current flow
• Initially
• High
• Opposite to charging
• Finally
• Zero
• Exponential model
• Discharging factors
• Capacitance
• Resistance
I t
• 10. Voltage and charge characteristics
• Charging Discharging
V or Q t V or Q t
• 11.
• Product of
• Capacitance of the capacitor being charged
• Resistance of the charging circuit
• CR
• Symbol  ‘Tau’
• Unit seconds
Time constant
• 12. When t equals tau during discharge
• At t = tau the capacitor has fallen to 37% of its original value.
• By a similar analysis tau can be considered to be the time taken for the capacitor to reach 63% of full charge.
• 13. Graphical determination of tau
• V at 37%
• Q at 37%
• Compared to initial maximum discharge
V or Q t
• 14. Logarithmic discharge analysis
• Mathematical consideration of discharge
• Exponential relationship
• Taking natural logs equates expression to ‘y=mx+c’