Physics (Theory) There are 30 questions in total. Question Nos. 1 to 8 are very short answer type questions and carry one mark each.

Transcription

1 Physis (Theory) Tie allowed: 3 hours] [Maxiu arks:7 General Instrutions: (i) ll uestions are opulsory. (ii) (iii) (iii) (iv) (v) There are 3 uestions in total. Question Nos. to 8 are very short answer type uestions and arry one ark eah. Question Nos. 9 to 8 arry two arks eah, uestion 9 to 27 arry three arks eah and uestion 28 to 3 arry five arks eah. There is no overall hoie. However, an internal hoie has been provided in one uestion of two arks; one uestion of three arks and all three uestions of five arks eah. You have to attept only one of the hoie in suh uestions. Use of alulators is not peritted. However, you ay use log tables if neessary. You ay use the following values of physial onstants wherever neessary: = 3 8 s h = Js e =.62 9 C = 4 7 T N C 4 Mass of eletron e = 9. 3 kg Q. Two wires of eual length, one of opper and the other of anganin have the sae resistane. Whih wire is thiker? Sine the resistivity of alloy is greater than the resistivity of its onstituents. We have resistivity of anganin greater than resistivity of opper etal. l So, Resistane R Where l is length and is area of ross-setion of aterial. lso is the resistivity of the aterial. l For opper, R l and for agnanin R We have

2 or l l s Dividing R R gain R = R Hene > Or, Manganin wire is thiker. Q 2. What are the diretions of eletri and agneti field vetors relative to eah other and relative to the diretion of propagation of eletroagneti waves? Sine eletroagneti waves are transverse in nature. We have eletri and agneti fields assoiated with an eletroagneti wave perpendiular to eah other and perpendiular to the diretion of propagation of eletroagneti waves. Let the diretion of eletri field and agneti field is along Y- and Z- axis then the diretion of propagation of EM waves will be in positive X-axis. Q 3. How does the angular separation between fringes in single-slit diffration experient hange when the distane of separation between the slit sreens is doubled?

3 We know angular separation is given as D d D D d Sine is independent of D, the distane of separation between the sreen and the slit so when D is doubled, angular separation would reain sae. Q 4. bar agnet is oved in the diretion indiated by the arrow between two oils PQ and CD. Predit the diretions of indued urrent in eah oil. ording to Lenz s law the polarity of the indued ef is suh that it opposes the hange in agneti flux responsible for its prodution. Sine North Pole of bar agnet is reeding away fro the oil so the right end of the oil will develop South Pole i.e. indued urrent as seen fro the left end will be antilokwise. gain, sine South Pole is pushing towards the seond oil so the left end of the oil will develop South Pole in order to repel it and derease the flux i.e. indued urrent as seen fro the left end will be lokwise.

4 Q 5. For the sae value of angle of inidene, the angles of refration in three edia, B and C are 5 O, 25 O and 35 O respetively. In whih ediu would the veloity of light be iniu? s light travels fro a rarer to denser ediu it bends towards the noral as its speed dereases. So, if the bending is ore, the speed of the light would be less in that ediu, opared to other edia. s the angle of refration is easured with respet to the noral, the ray aking the least angle of refration would bend ore and the speed of light would be iniu in that ase. So, the orret option is ediu where refrating angle is 5. Q 6. proton and an eletron have sae kineti. Whih one has greater de-broglie wavelength and why? Sine de-broglie wavelength in ters of kineti energy is given as h 2E k Where E k is kineti energy, is ass of eletron and h is the Plank s onstant. Thus for eletron and proton with sae kineti energy, de Broglie wavelength would depend on ass. Sine Now p > e so, e > p. Hene wavelength of eletron is greater than wavelength of proton. Q 7. Mention the two harateristi properties of the aterial suitable for aking ore of a transforer. Sine due to iron ore we have two types of losses,. Iron loss i.e. energy loss in the for of heat due to the indued eddy urrent that an be iniized by using thin lainated ore.

5 2. Hysteresis loss due to alternately passing a urrent in the oil to agnetize and deagnetize the iron ore. This an be redued by using a speial alloy of iron ore with silion. So aterial with less iron loss and less hysteresis loss is used for aking ore of transforer. Q 8. harge is plaed at the entre of a ube of side l. What is the eletri flux passing through eah fae of the ube? By using Gauss s Law. It is given as E ds Now, the flux passing through all the six surfaes would be 6 nd the flux passing through eah surfae would be 6