eLFH - Resistance, Inductance and Capacitance elements in circuits

Question 1

Capacitance (C) definition

Answer 1

Ability of an object to store electrical charge

Equal to charge per unit voltage
C = Q / V

Question 2

Units of Capacitance (C)

Answer 2

farad (F)

Normally use microfarads as the farad is very large

Question 3

Capacitor definition

Answer 3

Pair of conducting plates separated by space filled with an insulator (e.g. air)
Charge is stored on proximal plate with equal and opposite charge induced on opposite plate

On switch closure with direct current, proximal plate potential increases in inverses exponential and plateaus at maximum charge

Current has inverse exponential decrease and current stops flowing once maximal voltage difference in capacitor is reached

Question 4

Inductance (L) definition

Answer 4

The tendency of a conductor to induce an electromotive force or voltage that opposes the voltage drop due to circuit resistance

Question 5

Unit for inductance (L)

Answer 5

Henry (H)

Question 6

Inductor definition

Answer 6

Any wire carrying current has associated magnetic field

Inductor is a coiled wire - results in voltage induction which opposes the main voltage drop
Induced voltage is proportional to the rate of change of the current flowing through the coil

Closure of the switch with DC, initial voltage drop across inductor induces magnetic field and produces opposing electromotive force which reduces the voltage across the inductor and limits rate of change of the current flow

Question 7

Examples and function of low pass electronic filters

Answer 7

RC circuit
LR circuit

Acts as mathematical integrator - blocks high frequency signals and allows low frequency signals to pass

Question 8

Examples and function of high pass electronic filters

Answer 8

CR circuit

Cleans up ‘noisy signals’ - blocks low frequency signals and only allows high frequency signals to pass

Question 9

Band pass filter definition

Answer 9

Allows through signals within a specified bandwidth, blocking high and low frequency signals

Used in ECG monitors

Question 10

Reactance definition

Answer 10

Frequency-dependent resistance in circuit

Question 11

Impedance definition

Answer 11

Combination of reactance and resistance in circuit

Seen in LCR circuits

Question 12

Resonant frequency in LCR circuits

Answer 12

At resonant frequency ‘r’ for the circuit, the reactance is at a minimum and Vout/Vin is at a maximum

Question 13

Tuned circuit requirements

Answer 13

LCR circuit

Associated with a minimum output impedance
Frequency associated with maximum Vout/Vin