Posted: September 18th, 2017

# Fundamental Electrical Principles

PART A (150 words): Fundamental Electrical Principles (45%)

A1. We apply a voltage of 12 Volts to the terminals of a resistor of 16 . Assuming that it is part of a closed circuit without any other resistors calculate the following:
a) The intensity of the current. [2 marks]
b) The rate at which the energy is dissipated in the resistor. [2 marks]
c) If the current flows towards a terminal which has an electric potential of 7 Volts, what is the electric potential of the other terminal? [2 marks]
d) Now assume that we connect an identical resistor parallel to the original one. What is the new current intensity? [4 marks]

Α2. The battery in the circuit below has an electromotive force E=12 V and an internal resistance r=0.5 Ω. If resistors R1=40Ω and R2=60Ω calculate the following:

a)The intensity of the current through the battery. [2 marks]
b)The voltage at the terminals of the battery. [2 marks]
c)The total power that the battery provides to the circuit. [2 marks]
d)The intensity of the current through R2. [4 marks]

Α3. How would you construct a simple DC motor? Include pictures and formulas illustrating the operating principle of the device. Also, give a practical example of use of a DC motor. Make sure to cite your sources. [10 marks]

A4. The battery of the circuit below has an electromotive force E=24 V and an internal resistance r=0.7 Ω (not shown in the diagram). Determine:
a)The equivalent resistance of the circuit. You must show any intermediate steps you take explaining your actions. [10 marks]
b)The voltage at the terminals of the battery and the terminals of the 10  resistor. [5 marks]

PART B (350 words): Application of Electrical Principles (50%)

B1. You have been assigned to construct a DC electrical circuit which must provide power to three identical small decorative incandescent light bulbs with power needs between 5-10 Watts each. Electric power is provided by a battery. You are free to determine the circuit elements as you see fit.
You should write a brief report (approx 200-250 words) with the following elements:
a)A simple pictorial diagram (illustration) where you will be showing the components of the circuit (cables, switch, power source, light bulbs, etc) and their connections. [5 marks]
b)A technical diagram (schematic) of the electrical circuit where you will be using appropriate components and values. You are free to set any values you wish as long as they are in agreement with the power requirements of the bulbs. You should show your calculations and explain the steps you take. [15 marks]
c)Place appropriate instruments in your circuit to measure voltage and current intensity at the terminals of the light bulbs. Do these instruments affect the measurements? Explain your reasoning. [5 marks]
Note that you are not expected to give technical details about the lamps apart from their power needs and resistances.

B2. Construct two separate electrical circuits: one with an equivalent resistance of 60  and one with an equivalent resistance of 20 . [15 marks]
• In each circuit you must use at least 7 resistors.
• Use parallel and series connections in both circuits.
• The two circuits should use different resistors.
• You may assume that the internal resistance of the sources is negligible.
• In each case you should show your calculations.

B3. Apply electrical principles to determine the intensity of the current through R3 in the circuit below. The following values are given: E1=12 V, r1=2 , E2=10 V, r2=1 , R1=10 , R2=8 , R3=5 . [10 marks]

-End of Questions-

Module lecture and support notes.