Internal resistance and matching in voltage sources

Principle

Both the terminal voltage of a voltage source and the current depend on the load, i. e. on the external resistance. The terminal voltage is measured as a function of the current and from it the internal resistance and no-load voltage of the voltage source are determined and the power graph plotted.

Tasks

To measure the terminal voltage Ut of a number of voltage source as a function of the current, varying the external resistance Re, and to calculate the no-load voltage U0 and the internal resistance Ri.

1.1 Slimline battery

1.2 Power supply

1.2.1 Alternating voltage output

1.2.2 Direct voltage output

To measure directly the no-load voltage of the slimline battery (with no external resistance) and its internal resistance (by power matching, Ri = Re).

To determine the power diagram from the relationship between terminal voltage and current, as illustrated by the slimline battery.

What you can learn about

Voltage source
Electromotive force (e.m.f.)
Terminal voltage
No-load operation
Short circuit
Ohm's law
Kirchhoff's laws
Power matching

  Wheatstone Bridge

Principle

The Wheatstone bridge circuit is used to determine unknown resistances. The total resistance of resistors connected in parallel and in series is measured.

Tasks

Determination of unknown resistances.

Determination of the total resistance of resistors in series, of resistors in parallel.

Determination of the resistance of a wire as a function of its cross-section.

What you can learn about

Kirchhoff's laws
Conductor
Circuit
Voltage
Resistance
Parallel connection
Series connection

  Measurement of low resistances

Principle

The resistances of various DC conductors are determined by recording the current / voltage characteristic. The resistivity of metal rods and the contact resistance of connecting cords are calculated.

Tasks

To plot the current / voltage characteristics of metal rods (copper and aluminium) and to calculate their resistivity.

To determine the resistance of various connecting cords by plotting their current / voltage characteristics and calculating the contact resistances.

What you can learn about

Ohm's law
Resistivity
Contact resistance
Conductivity
Four-wire method of measurement

  Measuring range extension of a voltmeter

Principle

A sensitive moving coil galvanometer only has a very small measuring range when it is used directly as a voltmeter. With the aid of this educationally designed instrument, the measuring range can be extended by means of resistors connected in series in front of it.

  Ohm's Law

Principle

The connection between electrical voltage and the resulting current is measured with various test resistors.The quotient of voltage and current is a constant value that characterises the component.

  The Bimetallic Switch

Principle

A bi-metal strip comprises two metal strips which are laminated together and have different thermal expansion coefficients. When warmed the strip flexes toward the side with the lower expansion coefficient. In so doing, it can act as a switch in the electric circuit.

  Conductors and Non-Conductors

A.