Electrical Conduction and Potentials

4 Point Method / Measurement of low resistancesOhm's Law

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

1. To plot the current / voltage ...

Kirchhoff's laws

Principle

First Kirchhoff's laws are verified by measuring current, voltage and resistance in series and parallel circuits. The Wheatstone bridge circuit is used to determine unknown resistances more precisely.

Tasks

1. ...

Ion migration velocity

Principle

The movement of ions is responsible for current flow in solutions of electrolytes. The migration of coloured ions can be easily observed by the migration of the colour front in an electric field.

Tasks

Demons ...

Conductivity of strong and weak electrolytes (with the Cobra3 Basic-Unit)

Principle

It is possible to differentiate between strong and weak electrolytes by measuring their electrical conductance. Strong electrolytes follow Kohlrausch's law, whereas weak electrolytes are described by Ostwald's dilution law. The examination of the concentration depen ...

Determination of diffusion potentials

Principle

An electrochemical potential establishes itself at the interface between two solutions of different ion concentrations. The magnitude of this is determined by the concentration ratio and the transference numbers of ...

Recording of nerve and muscle potentials by mechanical stimulation at the rear end of an earthworm (Cobra3)

Principle and tasks

To work on the following themes by measuring nerve and muscle potentials:

• the course of a biphasic action potential over time
• estimation of the conduction velocity
• coding of the stimulant intensity as frequency modulation ...

Recording of nerve and muscle potentials by mechanical stimulation at the front end of an earthworm (Cobra3)

Principle and tasks

To work on the following themes by measuring nerve and muscle potentials:

• The difference in sensitivity of the front and rear ends
• The facilitation effect
• Conduction velocity and fibre diameter
• Synaptic depress ...

Recording of nerve potentials after the electrical stimulation of an anaesthetised earthworm (with the Cobra3 Basic-Unit

Principle and tasks

To work on the following themes by measuring nerve and muscle potentials:

• The action of an anaesthetic
• The different conduction velocities of median and lateral giant fibres
• Refractory period of the median giant fibre

Model experiment illustrating the development of resting potential (with Cobra4)

Principle and tasks

The potential difference between two electrolyte concentrations separated by a membrane (cellophane or cation permeable) is detected by two silver chloride electrodes and measured with a mV meter. The measured and calculated values are compared.

Human electrocardiography (ECG) (with the Cobra3 Basic-Unit)

Principle and tasks

To record an electrocardiogram (ECG) between the left leg and the right and left arm (lead II according to Einthoven). To relate the ECG segments to the course of heart contraction (P wave, P-Q segment, QRS complex, T wave).