Definitions and Simple Circuits

Question 1

What is the relationship between electrical charge and electrical current?

A. They are the same
B. Charge is rate of change of current
C. Charge is flow of current
D. Charge is electrons; current is positrons
E. Current is rate of change of charge

Answer 1

E. Electrical current is the flow of charge, or the flow of electrons, or the rate of change of electrons per unit of time.

A. Incorrect. They are not the same.

B. Incorrect. Current is rate of change of charge.

C. Incorrect. Current is flow of charge.

D. Incorrect. Charge is the quantity of electrons; current is rate of flow of electrons.

Question 2

In terms of the laws governing current flow and voltage distribution, what is the difference between a series circuit and a parallel circuit?

A. In a series circuit, the same current flows round the whole circuit
B. In a parallel circuit, the same current flows round the whole circuit
C. Uniquely in a series circuit, V = I/R
D. In a parallel circuit, the circuit resistance is the sum of the individual resistances

Answer 2

A.

Question 2

What is the difference between voltage and electromotive force (EMF)?

A. EMF is a way of describing the driving voltage from a battery
B. EMF is with reference to the battery’s power; voltage is with reference to electrical earth
C. They have different units
D. EMF requires an inductance; voltage requires a resistance
E. There is no difference

Answer 2

A. EMF is a way of describing the driving voltage from a battery.

B. Incorrect. EMF and voltage are both electrical potentials with reference to earth.

C. Incorrect. Both are potentials, and have units of volts.

D. Incorrect. The definitions of voltage and EMF do not depend on which elements are in the circuit.

E. Incorrect. They are both a form of electrical potential, but EMF describes a driving potential, while voltage usually refers to a drop in potential.

Question 3

What is the purpose of a Wheatstone bridge?

A. To provide a form of damping in an arterial waveform
B. To amplify a signal
C. To shunt mains currents to earth
D. To reject noisy signals common to both arms of the bridge
E. To act as a low pass filter

Answer 3

D. A Wheatstone bridge is a double bridge circuit designed to allow signals common to both arms to remain undetected and to allow a possibly much smaller signal (such as an arterial waveform from a strain gauge transducer) to be detectable at a meter applied between the two arms of the bridge.

Question 4

Which way does current flow?

A. From positive to negative
B. From negative to positive
C. From high potential to low potential
D. From capacitors to resistors
E. From resistors to inductors

Answer 4

B & C. Although it is easy to think of current flowing from the positive to negative terminals on a battery, current is actually electron flow and is from negative to positive as they are negatively charged particles. This anomaly does not make any difference in the analysis of circuits.

Question 5

Define Ohm’s law.

Select all those that apply:
A. Voltage is directly proportional to current
B. V = I/R
C. V = I x R
D. Resistance is the ratio of voltage to current
E. R = V/I

Answer 5

All except B.

Ohm’s law is

V = IR

or

R = V/I

Voltage is directly proportional to current; resistance is the ratio of voltage to current.

Question 6

A circuit contains two parallel resistances of value 300 Ω and 3 kΩ. What is the total value of the circuit resistance?

Select all those that apply:
A. 3.3 kΩ
B. 272.7 Ω
C. 333 Ω
D. 0.273 kΩ
E. 27.3 Ω

Answer 6

B & D.

The two resistances, R1 and R2, are in parallel; therefore, the total resistance of the circuit R is given by the calculation:

I = V1/R1 + V2/R2 + V3/R3

= V (1/R1 + 1/R2 + 1/R3)

= V/R where R is total circuit resistance

Therefore,

1/R = 1/300 + 1/3000

1/R = 10/3000 + 1/3000 = 11/3000

R/1 = 3000/11 = 272.7 Ω or 0.273 kΩ

Question 7

Which of the following is correct in relation to how a Wheatstone bridge works?

Select all those that apply:
A. All four resistances must be equal
B. It is a pair of potential dividers connected in parallel
C. Only one resistance is ‘active’
D. With a means of detecting any potential difference between its two parallel arms, the effect of unwanted voltages common to both arms is eliminated
E. It helps to eliminate signals common to both arms

Answer 7

B, D & E.