The energy gaps between the valence and conduction bands are called band gaps. for silicon, the band gap is 1.1 ev; for fused silica glass, it is 9.3 ev.
what is the wavelength λ of a photon that has energy 1.1ev?
the cut off between visible and infrared light is usually said to be somewhere between 700 and 800nm. why is silicon transparent to most infrared light but opaque to visible light?
a) visible photons have greater energy than the gap, so they can be absorbed whereas infrared photons pass through.
b) visible photons have greater energy than the gap, so they can’t interact with the silicon as the infrared photons can.
c) infrared photons have less energy than the gap, and so, unlike visible photons, they can be absorbed and reemitted from the material.
d) infrared photons have less energy than the gap, and so they are only partially absorbed whereas visible photons are fully absorbed.

First, launch the video below. you will be asked to use your knowledge of physics to predict the outcome of an experiment. then, close the video window and answer the question at right. you can watch the video again at any point. part a as in the video, we apply a charge +q to the half-shell that carries the electroscope. this time, we also apply a charge –q to the other half-shell. when we bring the two halves together, we observe that the electroscope discharges, just as in the video. what does the electroscope needle do when you separate the two half-shells again? view available hint(s) as in the video, we apply a charge + to the half-shell that carries the electroscope. this time, we also apply a charge – to the other half-shell. when we bring the two halves together, we observe that the electroscope discharges, just as in the video. what does the electroscope needle do when you separate the two half-shells again? it deflects more than it did at the end of the video. it deflects the same amount as at end of the video. it does not deflect at all. it deflects less than it did at the end of the video. submit

Thomas his older brothers, who own a junk yard, on the weekends to earn extra money. he likes to them push broken-down cars to the back of the junk yard because it makes him feel strong. last saturday, they pushed three cars with different weights, and he noticed he used different amounts of force for each one. the cars were the following weights: white car: 2,700 kg red car: 1,500 kg blue car: 2,100 kg think about how much force is needed to move each car. which correctly lists the cars in order from the most to least amount of force needed to move them? a) white, blue, red b) blue, red, white c) red, white, blue d) white, red, blue

An electron in an x-ray machine is accelerated through a potential difference of 1.00 × 104 v before it hits the target. what is the kinetic energy of the electron in electron volts?