1. Xtra Edge February 2012 - Career Point

MOCK TEST-3 (SOLUTION)
PHYSICS
1. There are many atoms in an atomic hydrogen gas
sample and electrons of different atoms can make
different transitions and different wavelength
radiations are emitted.
2. Frequency remains constant when light passes from
one medium to other.
3. Those sources which have constant phase difference
are called coherent sources. These are derived from
a single sources.
4. Kinetic energy depends on frequency of incident
radiations not on intensity so kinetic energy remains
same.
5. Average power over a complete cycle of ac through
an ideal inductor (Resistance = 0) is zero.
Pav = (Irms) × (Vrms) cos φ
R
cos φ = = 0
Z
Pav = 0
6. A
1A 2Ω 1Ω
+ –
B
VA – VB = 1 × 2 + 2 + 1 × 1 = 5 V
7. X–rays –→ 3 × 10 19 to 1 × 10 16 Hz
Microwave –→ 3 × 10 11 to 1 × 10 9 Hz
U-V rays –→ 5 × 10 17 to 8 × 10 14 Hz
Radio Waves –→ 3 × 10 7 to 3 × 10 4 Hz
8. φ = → →
q
E . A , ∆ φ =
ε
φi = EA cos 180° φf = EA cos 0°
φi = – EA φf = + EA
φi = – 5 × 10 5 V– m φf = 4 × 10 5 V– m
– 5 × 10 5 + 4 × 10 5 =
q
0
ε 0
, q = – ε0 × 10 5 Cb
9. Intensity of radiations is 64 = 2 6 times the safe value.
So after six half lines it would be safe so
t = 6T = 6 × 2 = 12 hours.
MOCK TEST– 3 PUBLISHED IN SAME ISSUE
10. On temperature rise more valance band electrons
become free and more free electrons and hole pair
will be produced and conductivity of semiconductor
increases.
11. In optical fibres refractive index of cladding is less
than core. So that electromagnetic wave traveling in
core when incidents other cladding at an angle
greater than ic. Total internal reflection will occur
which is necessary for transmission of signals from
one place to other.
12. Object should be placed at 2F of convex lens so as to
form image of same size. It can't happen in case of
concave lens because it always forms a diminished
image.
13. Using d = 2 Rh T + 2Rh
R
= R ( h h )
2 T R +
= 20.8 5 km = 46.5 km
14. When a charge +Q is given to the insulated plate,
then a charge –Q is induced on the nearer face of the
plate.
+ Q – Q
XtraEdge for IIT-JEE 88 FEBRUARY 2012
E
Net electric field between the plate
σ V
E = also, E =
ε0
d
∴ V = Ed =
with dielectric. C' =
σ d Q ε0A
= ⇒ C =
ε C d
0
ε0ε
A
r
d