Electricity

Question 1

How is capacitance measured?

Answer 1

In Farads (F). 1 farad = 1 coulomb per volt (large amount). Most practical capacitors have smaller values; e.g. defib in micro-farads.

Question 2

Stored energy of capacitor given by which formula?

Answer 2

E= 1/2 C(V squared)

Question 3

What is an inductor?

Answer 3

Electrical component consisting of a coil of conducting material wrapped around a coil of ferromagnetic material or air. Can store energy in a magnetic field created when a current passes through.

Question 4

What is inductance (L)?

Answer 4

Induction of voltage in a current-carrying wire where the current in the wire itself is changing. Measured in Henries (H).
High peak currents associated with myocardial injury.

Question 5

Where are inductors commonly found?

Answer 5

Often in defibrillators- create heavily damped sinusoids waveform (Lown waveform) of finite duration (~5 ms).

Question 6

Is inductive reactance small at low frequencies?

Answer 6

True; and large at high frequencies. For steady DC, inductive reactance is zero; hence inductors pass DC but block high frequency AC.

Question 7

Capacitors reactance is low at low frequencies?

Answer 7

False: large at low frequencies. Small at high frequencies. For steady DC, capacitor reactance is infinite. Hence capacitors pass AC but block DC.

Question 8

What is a transformer?

Answer 8

A device which utilises the principal of induction to adjust levels of voltage and current. It transfers energy from one circuit to another.

Question 9

In a transformer, if the primary circuit coils are greater in number than the secondary, what happens?

Answer 9

Electromotive force (EMF) generated is less than the supply EMF, hence forms a step-down transformer.