NCERT Solutions for Class 9th Science Chapter 8 .2.2 A. Rutherford's model of an atom — Think as a Scientist
Book page 1448 Updated on2026-09-08
Q1.
Observe Fig. 8.4 of the gold foil experiment. Predict the observations you would expect if the gold foil in the experiment were made thicker. Also, draw a simple diagram to show the observations you expect. Hint: Compare thin foil vs thick foil. How does the thickness affect the chances of hitting a nucleus?
Answer
Prediction: more deflection and less transmission. With a thicker foil you would see
fewer α-particles passing straight through undeflected;
more α-particles deflected, and more of them deflected through large angles;
a larger fraction bouncing back towards the source;
many particles arriving at odd angles because they were deflected more than once on the way through.
Why. A thicker foil means more layers of gold atoms along the α-particle's path. Each extra layer is one more chance of passing close to a nucleus. If the chance of a significant deflection in one layer is small, the chance of escaping all the layers untouched falls as the number of layers rises.
Thin foil vs thicker foil. With more layers of gold atoms in the path, fewer α-particles get through untouched and more are deflected — some of them more than once.
Why it happens: this is exactly why Geiger and Marsden used an extremely thin foil — only a few hundred atoms thick. In a thin foil, an α-particle that is deflected has almost certainly been deflected once, by a single nucleus. That lets you work backwards from the angle to the size and charge of the scatterer. In a thick foil the multiple deflections pile up and the information is lost.
Check it yourself: the conclusion “the atom is mostly empty space” comes from the fact that most particles went straight through. If a thick foil stopped most of them, would that disprove the nucleus? No — it would only mean the beam met more nuclei. The physics of one collision has not changed.