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title: "The first transistor: a small input controlled a larger current"
description: "What did the point-contact experiment demonstrate that an ordinary resistor could not?"
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Materials · Measurements · Explanation

# The first transistor: a small input controlled a larger current

What did the point-contact experiment demonstrate that an ordinary resistor could not?

Sandbox Physics · 2026-10-23

Nobel contribution: 1956-1

1. Place two contacts on germanium
2. Inject carriers near the surface
3. Bias a separate output
4. Measure signal gain

The output power came from the bias supply. Carrier injection controlled how that power reached the signal.

## Two close contacts changed the experiment

In December 1947, Bardeen and Brattain used nearby point contacts on germanium to obtain amplification. Surface states had frustrated a simple field-effect approach, and the working device made the semiconductor surface an active part of the investigation.

Shockley’s subsequent junction-transistor theory offered another route to controlling carriers. The joint 1956 award covers semiconductor research and the transistor effect; it does not make the point-contact and junction devices identical.

Sources: [1] [2]

## Gain must be measured in a biased circuit

A change at the input modifies carriers collected by a separately biased output. Voltage and current measurements establish gain only after the source and load are specified. A passive resistance change alone cannot supply amplified signal power.

Sources: [1] [2]

## Junction output curves reveal useful operating ranges

In a junction transistor, a thin base allows many injected minority carriers to reach the collector. Output curves distinguish an active region from cutoff and saturation. Gain changes with bias and device construction, so it is not a universal material constant.

Sources: [2]

## The new Lab follows the junction device

The output-characteristics Lab connects carrier control to a collector-current sweep. Its junction model explains bias and saturation. The historical point-contact result remains a separate experiment whose geometry and surface physics are described in the original accounts.

Sources: [1] [2] [3]

Continue with the physics

## Try the related models

### [Transistor output curves](https://sandboxphysics.com/labs/transistor-output-characteristics/)

Change base injection and measure collector current.

The junction-transistor teaching model differs from the original point-contact device.

## Sources and reading notes

1. [Bardeen: Semiconductor research (1956)](https://www.nobelprize.org/uploads/2018/06/bardeen-lecture.pdf)

   Surface states, the failed field-effect approach and the route to point-contact amplification.

2. [Shockley: Transistor technology evokes new physics (1956)](https://www.nobelprize.org/uploads/2018/06/shockley-lecture.pdf)

   Junction devices and carrier injection; distinguish them from the 1947 point-contact experiment.

3. [Nobel Prize in Physics 1956: official award](https://www.nobelprize.org/prizes/physics/1956/summary/)

   Official attribution and award year. The observation or theoretical paper may be much earlier.

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