You are Here: Home

# Moving up and Down watch

Announcements
1. ( Oscillations )

A Simple model of a crystal assumes that the atoms in it are vibrating in the same way as the mass in a mass - spring system. The inter atomic bonds behave like the springs and have a spring constant ' k '

In one instance, an atom in a crystal lattice vibtates with simple harmonic motion of frequency 1 x 10 ^ 13 . The energy of an atom at room temperature is approx 4.2 x 10 ^-21

1) Calculate the max velocity of an atom of mass 3.7 x 10 ^ - 26 kg when trapped in a crystal lattice at room temperature

2) Determine the amplitude of the oscillation of the atom

3) When radiation of different frequencies falls on the crystal, one frequency is absorbed because it causes a sharp resonance

what is meant by resonance?

4) Explain why atoms are likely to have a sharp resonance whereas resonance of a mass spring system is unlikely to be sharp
2. hi ok for the first question it gives you the mass as well as the kinetic energy

as soon as these two words appear in my mind i think Ek = 1/2 mv 2 the eq. you should know back to front

therefore Ek = 1/2 mv2
4.2 x 10^-21 = 1/2 x 3.7 x 10^-26 x v2

then v2 = 4.2 x 10-^21 / 1/2 x 3.7 x 10^-26

SQUARE ROOT THAT to get v on its own which gives 476.5 ms-1

for the second.... it wants the amplitude so use the equation V = WA ( w is angular speed )

therefore A = V / W

you already worked out the speed from the previous question, therefore you need W

**** it doesnt give u W but you can use 2 pi F instea

therefore speed / 2 pi F which gives you an answer of 7.58 x 10^-12 m

ok the third one i just remmeber these definitions, you have to

so res is like the period driving force that makes the amplitude of oscillation the largest i.e. if i push a ruller up and down on a table im NEVER EVER gonna be able to reach its natural frequency..... if i push it and let go it will vibrate like no other

ok.... the last question

the atoms are not gonna experience frictional forces or air resistance as such and that frictional forces cause damped oscillations ( damped oscillations occur and DECREASE THE BODIES ENERGY - due to friction etc ) like if you sit on a cars suspension
3. DazzYaa00 cheers mate
4. (Original post by Tripple)
DazzYaa00 cheers mate
word.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: June 4, 2004
Today on TSR

### University open days

1. Norwich University of the Arts
Fri, 28 Sep '18
2. Edge Hill University
Faculty of Health and Social Care Undergraduate
Sat, 29 Sep '18
3. Birmingham City University