Physics - Paper II - For Class XII (Science Group) - Model papers With Solved MCQs 2020 -2021

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Physics - Paper II
For Class XII (Science Group)
Model papers 2020 -2021

The correct answer of number mcqs no. (xix) is waxed paper

SECTION "B" (SHORT ANSWER QUESTION) (28 Marks)

Q.2(i):
Data:
R_g = 50 Ω
I_g = 5 mA = 5 x 10^-3 A
R_x = 0.1 MΩ = 0.1 x 10⁶ Ω
v =?

Formula:
R_x = ^-V / _Ig - R_g
R_x + R_g = ^-V / _Ig
Or
V = I_g(R_x + R_g)

Solution:
V = 5 x 10^-3 (0.1 x 10⁶ + 50)
V = 5 x 10^-3 (100000 + 50)
V = 5 x 10^-3 (100050)
V = 500250 x 10^-3
V = 500.25 V Ans

Q.2(ii):
Data:
d_i = 5 cm
ΔL = 0.01 mm = 0.01 / 10 = 0.001 cm
ΔT = 30 °C
α_i= 1.2 x 10^-5 C^-1
α_b= 1.9 x 10^-5 C^-1

Formula:
ΔL = αL_o ΔT

Solution:
ΔL_i = α_i d_i ΔT
ΔL_b = α_b d_b ΔT
ΔL = ΔL_i - ΔL_b
d_i ≅ d_b

0.001 = α_i d_i ΔT - α_b d_i ΔT
0.001 = d_i (α_i - α_b) ΔT
0.001 = 5 (1.2 x 10^-5 - 1.9 x 10^-5) ΔT
ΔT = 0.001 / 5 x 0.7 x 10^-5
ΔT = 28.5 °C

Final temperature
T = 28.5 + 30
T + 58.5 °C Ans


Q.2(iv):
Data:
R_H = 1.0967800 x 10⁷ m = 1.097 x 10⁷ m
n_f = 2 (Balmer)
a) n_i = 3 (Largest)
b) n_i = ∞ (Shortest)
λ_max = ?
λ_min = ?

Formula:
¹/ _λmax = R_H ( ¹/_nf² - ¹/_ni²)
¹/ _λmin = R_H ( ¹/_nf² - ¹/_∞)

Solution:
For Longest Wavelength

Q.2(v):
Data:
m = 2m_o
a) V =?
b) P = ?

Q.2(vi):
Data:
Number Of Bulbs = b = 5
Power Of Bulb = P_b = 100 W
Number Of Fans = f = 10
Power Of Fan = P_f = 60 W
Number Of Lights = l = 10
Power Of Light = P_l = 40 W
Number Of Iron = i = 1
Power Of Iron = P_i = 1000 W
Time = t = 4 x 30 x 60 x 60 = 432000 sec
Energy = E = ? (Kwh)
R = 90 paisa / unit
Cost = ?

Formula:
E = P x t
P = ^E / _F

Solution:
Total Power:
Bulb = P₁ = b x P_b = 5 x 100 = 500 W
Fan = P₂ = f x P_f = 10 x 60 = 600 W
Light = P₃ = l x P_l = 10 x 40 = 400 W
Iron = P₄ = i x P_i = 1 x 1000 = 1000 W

P = P₁ + P₂ + P₃ + P₄
P = 500 + 600 + 400 + 1000 = 2500 W

E = P x t
E = 2500 x 432000
E = 1.08 x 10⁹ J

1 kwh = 3600 000 J

E = ^{1.08 x 109} / _{36 x 10⁵}
E = 300 kwh Ans.

b) Cost
Cost = Kwh x Rate
Cost = 300 x 0.9
Cost = 270 Rs. Ans.




SOURCE: Board Of Intermediate Education Karachi