23.03.2013 Views

1. Xtra Edge February 2012 - Career Point

1. Xtra Edge February 2012 - Career Point

1. Xtra Edge February 2012 - Career Point

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

PHYSICS<br />

<strong>1.</strong> Refractive index is maximum for violet and<br />

minimum for red colour<br />

2. Path difference between two waves should be odd<br />

multiple of λ/2 or phase difference between two<br />

waves should be odd multiple of π.<br />

3.<br />

P<br />

−34<br />

h 6.<br />

6 × 10<br />

= =<br />

= <strong>1.</strong>32 × 10<br />

−10<br />

–27 kg-m/s<br />

λ<br />

5000 × 10<br />

4. R = R0A 1/3 ⇒ R ∝ A 1/3<br />

∴<br />

R 1<br />

=<br />

R 2<br />

⎛ A<br />

⎜<br />

⎝ A<br />

3R<br />

∴ R2 =<br />

2<br />

1<br />

2<br />

⎞<br />

⎟<br />

⎠<br />

1<br />

3<br />

⇒<br />

R<br />

=<br />

R 2<br />

1<br />

⎛ 8 ⎞<br />

⎜ ⎟⎠<br />

⎝ 27<br />

/ 3<br />

2<br />

=<br />

3<br />

5. It should be very high i.e. in KHz to GHz<br />

6.<br />

=<br />

µ<br />

c<br />

v ; v2 < v3 < v1<br />

7. Resistivity or specific resistance of a material is<br />

defined as the resistance offered by a wire made by<br />

that material having unit area of cross-section and<br />

unit length.<br />

W<br />

8. V = =<br />

q<br />

MOCK TEST-2 (SOLUTION)<br />

<strong>1.</strong><br />

6×<br />

10<br />

3.<br />

2×<br />

10<br />

– 5<br />

– 7<br />

MOCK TEST– 2 PUBLISHED IN JANUARY ISSUE<br />

= 50 volt<br />

9. Objective lens must have greater focal length than<br />

eye-piece because magnifying power of lens<br />

⎛ f ⎞<br />

⎜ 0 ⎟<br />

⎜<br />

M P =<br />

⎟<br />

increases in this case.<br />

⎝ fe<br />

⎠<br />

10. Conditions of interference<br />

(i) waves must travel in the same medium in the<br />

same direction.<br />

(ii) Their frequencies and wavelengths must be<br />

same<br />

(iii) Their plane of polarisation must be same<br />

(iv) Their must be maintained a constant phase<br />

difference between the waves.<br />

1<strong>1.</strong> Ionisation energy:- Minimum energy required to<br />

remove electron from its ground state.<br />

Excitation energy:- Energy required to transit an<br />

electron to one of its excited state from ground state<br />

KE =<br />

2r<br />

; U = –<br />

∴ U = −2KE<br />

<strong>Xtra</strong><strong>Edge</strong> for IIT-JEE 74 FEBRUARY <strong>2012</strong><br />

KZe 2<br />

12. Emax. = 12V; Emin. = 4V<br />

Ma =<br />

E<br />

E<br />

max<br />

max<br />

− E<br />

+ E<br />

min<br />

min<br />

KZe 2<br />

r<br />

12 − 4<br />

= =<br />

12 + 4<br />

1<br />

2<br />

1<br />

∴ ma in percentage = × 100 = 50%<br />

2<br />

13. Modulating signal being of low frequency cannot<br />

travel to large distance so it is modulated with high<br />

frequency carrier. Frequency modulation is virtually<br />

free from noise where as amplitude modulation<br />

suffers from noise pollution.<br />

14. Semiconductor atoms are tetravalent. The form<br />

covalent bonds by sharing their electrons with the<br />

neighboring atoms. When donor impurity of valency<br />

S is doped, the donor atoms takes the place of a<br />

semiconductor atom in the crystal lattice. Donor<br />

atoms forms covalent bond by sharing its four<br />

electrons whereas the fifth electron of donor atom is<br />

so loosely attached to the atom such that it behaves<br />

as a free electron at room temperature.<br />

15. (i) width of depletion layer of zener diode<br />

becomes very small due to heavy doping of<br />

p and n regions.<br />

(ii) The field across depletion layer becomes very<br />

⎛ V ⎞<br />

high ⎜Q<br />

E = ⎟<br />

⎝ d ⎠<br />

16. Let at any instant charge on the capacitor is q, then<br />

q<br />

p.d. V =<br />

C<br />

Then work done to put additional charge dq is<br />

⎛ q ⎞<br />

dW = (dq) V = ⎜ ⎟ dq<br />

⎝ C ⎠<br />

∴ Total work done to give charge Q is<br />

Q<br />

⎛ q ⎞ Q<br />

W = ∫⎜ ⎟dq =<br />

⎝ C ⎠ 2C<br />

2<br />

1 2<br />

= CV (Q Q = CV)<br />

2<br />

0

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!