Quizzes > Engp Q6 02

UNIVERSITY OF SOUTH AUSTRALIA Applied Physics - School of Electrical & Information Engineering ENGINEERING PHYSICS QUIZ 6 [ week 13 ] Time: 20 minutes

Name .....................................................................................

Marks:

QUESTIONS ( 8 MARKS )

/15

ANSWERS

1. What is the resistivity of an ideal wire?

A. Zero. B. This would be effectively infinite. C. This would be directly proportional to its length. D. This would vary inversely with its cross-sectional area.

2. With non linear optical techniques they can now produce fempto-second laser pulses. The prefix fempto represents … A. 10-9, B. 10-12,

C. D.

10-15, 10-18.

3. A permanent ceramic magnet is composed of … A. B. C. D.

Diamagnetic material, Paramagnetic material, Ferromagnetic material, High temperature super-conductors.

4. You have just purchased a good quality compass from the Australian National Geographic shop. The red end of the needle points north when in Adelaide. If the same compass is taken on a back-packing tour of Europe, A. it will not work at all, B. the red end will still point north, C. the red end will now point south, D. Assuming the compass only interacts with the magnetic field of the earth, any of these could be possible.

5. Which of the following statements about ferrimagnets is FALSE? A. B. C. D.

Ferrimagnets are mixed ceramic oxides of Barium or Strontium with Iron oxide, Ferrimagnets are mechanically hard but brittle, Ferrimagnets are light and electrically conducting, Ferrimagnets have adjacent molecular magnets aligned antiparallel but with unequal strength.

6. Which statement below is FALSE? A. B. C. D.

Y = FLo/A∆L S = Fh/A∆x, B = FVo/A∆V, none of the above.

7. The velocity of sound in water is… A. B. C. D.

dependant on the bulk modulus of water, dependant on the temperature of the water, greater than the velocity of sound in air, all of the above.

8. The Curie temperature of a material … A. B. C.

is the melting temperature of the material, is of interest if we wish to demagnetize the material, is the temperature at which the material becomes radioactive

PROBLEMS ( 12 Marks possible ) Question 1 (2 marks) You come across an APPLICATION PAPER titled “Faster Magnetic Memory” You read that “Researchers have found a high speed way to flip the alignment of atoms in a thin layer of magnetic material’…and… ‘Typically the ‘read/write head’ consists of a small coil of wire wound round a soft-magnet’ What do they mean by ‘soft-magnet’? and why use it? …………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………… Question 2 (4 marks) APPLICATION PAPER – “Micro-mechanics looks at superconductors” (a) Sketch and Label the resistivity versus temperature diagram for a superconducting metal and a normal metal.

Super conducting metal

normal metal

You also read that ‘but in so-called type-II superconductors, magnetic flux can penetrate the material below a certain field’ (b) What is the difference between type-I and type II superconductors? ie. define type-I & II superconductors. …………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………… Problem 1 (4 marks) An average person (mass 70kg) rock climbing slips from a ledge, hangs in free air from a slim nylon rope with a length of 20m, a cross sectional area of 1cm2, and a Young’s modulus of 1 x 1010 N/m2. What is the increase in length of the rope from it’s un-stressed form? ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..…………………………………………………………………………… ………………………………………..……………………………………………………………………………