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1. Xtra Edge February 2012 - Career Point

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This work done is stored inside the capacitor as P.E.<br />

1 2<br />

∴ U = W = CV<br />

2<br />

17. (i) A galvanometer can be converted into ammeter<br />

by connecting a low resistance called shunt parallel<br />

to the galvanometer coil.<br />

(ii) A galvanometer can be converted into voltmeter<br />

by connecting a large resistance in series with the<br />

galvanometer coil.<br />

18. (i) Electromagnetic waves are produced by<br />

accelerated charge.<br />

(ii) The velocity of electromagnetic wave in free<br />

space is equal to the velocity of light in free space.<br />

(iii) It is transverse in nature.<br />

19. α = 2º<br />

β = ?<br />

fo = 20 cm<br />

fe = 4 cm<br />

β<br />

MP = and MP =<br />

α<br />

⎛ 20 ⎞<br />

∴ β = ⎜ ⎟ × 2 = 10<br />

⎝ 4 ⎠<br />

20.<br />

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

f<br />

f<br />

o<br />

e<br />

∴<br />

β<br />

α<br />

f<br />

=<br />

f<br />

h<br />

λ =<br />

2mqV<br />

for proton<br />

h<br />

λ =<br />

…(i)<br />

2meV<br />

For α-particle<br />

h<br />

λ =<br />

…(ii)<br />

2×<br />

4m×<br />

2eV'<br />

By (i) and (ii)<br />

2meV = 2 × 4m × 2eV'<br />

V '=<br />

V / 8<br />

BE/A<br />

e<br />

d<br />

c<br />

b<br />

a<br />

Fe 56<br />

o<br />

e<br />

⎛ f<br />

⇒ β = ⎜<br />

⎝ f<br />

A<br />

o<br />

e<br />

⎞<br />

⎟<br />

α<br />

⎠<br />

a → 2He 4<br />

b → 4Be 8<br />

c → 6C 12<br />

d → 8O 16<br />

e → 10Ne 20<br />

22. 2 is NAND and 1 is OR gate<br />

A B Y' Y<br />

0 1 1 0<br />

23. R = (AB × 10 c ± 5)%<br />

Yellow A = 4<br />

Violet B = 7<br />

Brown C = 1<br />

∴ R = (47 × 10 ± 5)%<br />

= (470 ± 5)%<br />

24. (i) To make strong electromagnet<br />

(ii) To make high speed computers<br />

25. tanθ =<br />

<strong>Xtra</strong><strong>Edge</strong> for IIT-JEE 75 FEBRUARY <strong>2012</strong><br />

B<br />

B<br />

V<br />

H<br />

∴ BV = BH tanθ = 0.4 × 10 –4 tan60º = 0.69 × 10 –4 T and<br />

BH = Be cos θ<br />

⇒ Be =<br />

−4<br />

BH<br />

0.<br />

4×<br />

10<br />

=<br />

cosθ<br />

cos60º<br />

= 0.8 × 10 –4 T<br />

26. Biot–Savart′s law<br />

This law is applicable to determine magnetic field<br />

due to small current element. Magnetic field due to<br />

small element →<br />

d l at point A is given as<br />

i<br />

→<br />

dl →<br />

dl<br />

→<br />

r<br />

→ →<br />

→ µ 0i<br />

( dl×<br />

r<br />

=<br />

3<br />

dB<br />

4π<br />

µ 0 idl<br />

sin θ<br />

or dB =<br />

4π<br />

2<br />

r<br />

where µ0 ⇒ Permeability of free space,<br />

θ ⇒ between →<br />

d l and →<br />

r .<br />

27. (i) On increasing distance between the coils, flux<br />

linked decreases, hence mutual inductance decreases<br />

µ 0<br />

N1N2A (ii) Q M =<br />

l<br />

∴ on increasing no. of turns, M increases<br />

(iii) when iron sheet (µr) is inserted<br />

µ 0 µ rN1N<br />

2A<br />

Then M =<br />

l<br />

∴ M increased, because for iron µr > > 1<br />

r<br />

)<br />

A

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