2nd exam, 2007. forrásának megtekintése

{{GlobalTemplate|Infoalap|Angfiz2Vizsga2007}}

-- [[PappLaszlo|psigy]] - 2008.01.13.


==I. Problems (2 points each):==

====1. A current of 10A is flowing in a clockwise direction in a circular loop having a radius a = 2cm. Another current of 10A is flowing in the opposite direction in another, concentric circular loop having a radius b = 4.5cm. Find the magnetic field at the center.====
(a) 174&#61549;T		(b) 235&#61549;T		(c) 450&#61549;T		(d) none

<math>\sum B= |B_1 -B_2|</math>

<math> B_1= \frac {\mu_0*I_1}{2*r_1}	= 1,3962*10^{-4}		  </math>

<math> B_2= \frac {\mu_0*I_2}{2*r_2}	= 3,141*10^{-4}		  </math>


<math> B_2-B_1 = 1,74*10^{-4}		  </math>


*a*




====2. A long, straight wire carries a current of 10A. At a distance of 1cm from the wire a point charge of 100nC is moving perpendicularly to the wire with 106 m/s instantaneous speed. Find the Lorentz-force acting on the point charge at this point.====
(a) 0.02mN		(b) 0.1mN		(c) 1.65mN		(d) none

<math>\ B= \frac {\mu_0*I}{2*\pi*R}		 </math>

<math>F= Q*v*B</math>

*a*



====3. A current of 2A flows in a cylindrical wire having a radius of 1mm. How far from the axis of the wire (outside the wire) does the magnetic field have the same value as at a distance 0.5mm from the axis?====
(a) 1.25mm		(b) 1.5mm		(c) 2mm		(d) other

====4. Find the magnetic energy stored in a toroid whose central line is 1m long, the cross sectional area is 10cm2 and the current is 2A. The toroid has 1000 turns.====
(a) 0.46mJ		(b) 0.91mJ		(c) 2.52mJ		(d) none

====5. 10 turns of wire are tightly wound around a solenoid having a length of 12.56cm and a cross-sectional area of 5cm2. The number of turns of the solenoid is 200. Find the mutual inductance.====
(a) 5&#61549;H		(b) 10&#61549;H		(c) 15&#61549;H		(d) none

====6. Two slits at a distance of 0.4mm from each other are illuminated with blue light (&#61548;=400nm). Find the distance between the interference fringes if the screen is 1 meter away from the slits.====
(a) 1mm		(b) 2mm		(c) 10mm		(d) none

====7. Calculate the ratio between (1) the power incident on a 4mm2 surface at a distance 1 meter from a 25W light bulb, and (2) the power incident on the same surface if it is illuminated by a 1mW laser. The diameter of the laser beam is 1mm. ====
(a) 1/8			 (b) 1/53		(c) 1/126		(d) none

====8. An electron is confined to a 1D box in which its ground state energy is 2eV. How much energy is required to excite the electron into the next energy state?====
(a) 2eV		(b) 4eV		(c) 6eV		(d) none

====9. Determine the number of electrons that can occupy the n=3 shell in an atom.====
(a) 9			(b) 18			(c) 36			(d) none

====10. Find the smallest possible value of &#61553; &#61485; the angle between the orbital angular momentum vector and an external magnetic field &#61485; for an electron in a 3d state of hydrogen.====
(a) 35&#61616;			(b) 45&#61616;			(c) 55&#61616;			(d) none
 
==II. True-false statements (1 point each):					==

		
====1. According to Biot-Savart's law the magnetic field is inversely proportional to the cube of the distance from the current element.		====
F
====2. The flux of  for a closed surface is always zero.====
T		
====3. The Hall-effect can be a useful tool for measuring the magnetic field.	====
T	
====4. If the net current across a surface bounded by a closed loop is zero, then the magnetic field is zero everywhere along the loop.  ====
F	 
====5. Paramagnetic materials cannot be gases or liquids.====
F
====6. The line integral of the magnetic field strength can be measured in W/V.		====
T
====7. The mutual inductance depends on the applied current.====
F		
====8. In Young's double slit experiment, when the illumination is white light, the zeroth-order fringe is in color.		====
F
====9. When an incident light of any polarization comes at Brewster's angle, there is no reflection.====
F		
====10. The resolution of an astronomical telescope is independent of the observed wavelength. ====
F		
====11. In blackbody radiation, the total emitted power is proportional to the fourth power of the temperature. ====
T	  
====12. In blackbody radiation, the temperature multiplied by the maximal wavelength gives a universal constant.		====
F
====13. Natural line broadening in a laser can be explained using Heisenberg's uncertainty principle.		====
T
====14. Covalent bond is caused by the Coulomb attraction between two ions.		====
F
====15. Knowing the rotational energy levels of a molecule gives us information about the bond strength.		====
F
 
==III. Theory (3 points each):						  ==


====1. What interpretational difficulties arise in relation with the magnetic permeability of ferromagnetic materials?====

====2. How can we produce linearly polarized light out of unpolarized light? (List at least 2 or 3 different methods.)====

====3. Why are at least 3 energy levels necessary in optical laser pumping?====

====4. What is Wien&#8217;s displacement law of blackbody radiation?====

====5. What is the physical meaning of the square of the absolute value of the wave function?====



-

<math>q_e=1.6*10^{-19}C</math>	 

<math>m_e=9.1*10^{-31}kg	  </math>

<math> \mu_0=4\pi*10^{-7}\frac{Vs}{Am}	</math>  

<math>E_0=8.85*10^{-12}\frac{As}{Vm}	</math>  

<math>h=6.626*10^{-34}Js	</math>


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