Exercise EE1-03.K1

Prof. Dr. Thorsten Jungmann (last updated 2026-03-02)

Task 1: Types of sources and properties

Mark the correct statement(s):

a) An ideal voltage source has an internal resistance of zero ohms.

b) With a real current source, the output current remains absolutely constant regardless of the load voltage.

c) The open-circuit voltage of a real voltage source is equal to its source voltage.

d) The short-circuit current of a linear source is infinitely large.

Solution

a), c) are correct

Mark the incorrect statement(s):

a) The internal resistance of a real source limits the maximum power it can deliver.

b) With maximum power transfer, the efficiency is always 100 %.

c) An ‘empty’ battery often still shows the correct open-circuit voltage but has an increased internal resistance.

d) The terminal voltage of a loaded voltage source is lower than its open-circuit voltage.

Solution

b) is incorrect

Mark the correct statement(s):

a) The operating point of a linear electric circuit lies at the intersection of the source characteristic curve and the load characteristic curve.

b) The I-U characteristic curve of a linear source follows a sine function.

c) In the case of a short circuit, the terminal voltage is zero and the current is at its maximum.

d) Maximum power transfer occurs at $R_{L} = R_{i}$ .

Solution

a), c), d) are correct

Match the properties (left) to the source type (right):

Energy converter		Source type
A) Low internal resistance, practically constant terminal voltage in the operating range		1) Ideal voltage source
B) Low internal conductance, practically constant terminal current in the operating range		2) Real voltage source
C) No internal resistance, constant terminal voltage regardless of the load		3) Dependent source
D) No internal conductance, constant terminal current regardless of the load		4) Real current source
E) Source voltage depends on another input quantity		5) Ideal current source

Solution

A→2, B→4, C→1, D→5, E→3

Match the characteristic quantities of sources (left) to their meaning (right):

Characteristic quantity		Meaning
A) $U_{0}$		1) Current with short-circuited terminals
B) $I_{sc}$		2) Resistance inside the source
C) $R_{i}$		3) Voltage with open terminals
D) $u_{C}$		4) Power at the load
E) $G_{i}$		5) Voltage across the capacitor
		6) Reciprocal of the internal resistance
		7) Maximum efficiency

Solution

A→3 (open-circuit voltage), B→1 (short-circuit current), C→2 (internal resistance), D→5 (capacitor voltage), E→6 (internal conductance)

Match the descriptions (left) to the correct equivalent circuit concepts (right):

Description		Concept
A) Voltage source with series $R_{i}$		1) Norton equivalent circuit
B) Current source with parallel $G_{i}$		2) Superposition principle
C) $U_{0} = R_{i} \cdot I_{sc}$		3) Ohm’s law
D) $R_{L} = R_{i}$ for $P_{ma x}$		4) Equivalence of both equivalent circuits
E) $I_{sc} = U_{0} \cdot G_{i}$		5) Thévenin equivalent circuit
		6) Kirchhoff’s laws
		7) Maximum power transfer

Solution

A→5 (Thévenin), B→1 (Norton), C→4, D→7, E→4