12th Standard Physics English Medium Free Online Test Book Back one Mark questions

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Questions:

Multiple Choice Question

25 x 1 = 25

The blue print for making ultra durable synthetic material is mimicked from _____.

(a)

Lotus leaf

(b)

Morpho butterfly

(c)

Parrot fish

(d)

Peacock feather

The variation of frequency of carrier wave with respect to the amplitude of the modulating signal is called ______.

(a)

Amplitude modulation

(b)

Frequency modulation

(c)

Phase modulation

(d)

Pulse width modulation

The given electrical network is equivalent to ______.

(a)

AND gate

(b)

OR gate

(c)

NOR gate

(d)

NOT gate

A forward biased diode is treated as ________________.

(a)

An open switch with infinite resistance

(b)

A closed switch with a voltage drop of 0V

(c)

A closed switch in series with a battery voltage of 0.7V

(d)

A closed switch in series with a small resistance and a battery

The mass of a ₃⁷Li nucleus is 0.042 u less than the sum of the masses of all its nucleons. The binding energy per nucleon of ₃⁷Li nucleus is nearly _____.

(a)

46 MeV

(b)

5.6 MeV

(c)

3.9 MeV

(d)

23 MeV

In J.J. Thomson e/m experiment, electrons are accelerated through 2.6 kV enter the region of crossed electric field and magnetic field of strength 3.0 x 10⁴ Vm^-1 and 1.0 x 10^-3 T, respectively, and pass through it and undeflected, then the specific charge is _____.

(a)

1.6 × 10¹⁰ C kg^–1

(b)

1.7 × 10¹¹ Ckg^–1

(c)

1.5 × 10¹¹ Ckg^–1

(d)

1.8 × 10¹¹ Ckg^–1

A light of wavelength 500 nm is incident on a sensitive metal plate of photoelectric work function 1.235 eV. The kinetic energy of the photoelectrons emitted is_____. (Take h = 6.6 x 10^–34Js)

(a)

0.58 eV

(b)

2.48 eV

(c)

1.24 eV

(d)

1.16 eV

The wave associated with a moving particle of mass 3 x 10^–6 g has the same wavelength as an electron moving with a velocity 6 x 10⁶ ms^-1. The velocity of the particle is _____.

(a)

1.82 x 10^-18ms^-1

(b)

9 x 10^-2ms^-1

(c)

3 x 10^-31ms^-1

(d)

1.82 x 10^-15ms^-1

A plane glass is placed over a various coloured letters (violet, green, yellow, red) The letter which appears to be raised more is _____.

(a)

red

(b)

yellow

(c)

green

(d)

violet

10.

For light incident from air on a slab of refractive index 2, the maximum possible angle of refraction is, ______.

(a)

30^o

(b)

45^o

(c)

60^o

(d)

90^o

11.

Two short bar magnets have magnetic moments 1.20 Am² and 1.00 Am² respectively. They are kept on a horizontal table parallel to each other with their north poles pointing towards south. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid-point O of the line joining their centres is (Horizontal components of Earth’s magnetic induction is 3.6 × 10^–5 Wb m^–2 )

(a)

3.60 × 10^-5 Wb m^-2

(b)

3.5 × 10^-5 Wb m^-2

(c)

2.56 × 10^-4 Wb m^-2

(d)

2.2 × 10^-4 Wb m^-2

12.

The BH curve for a ferromagnetic material is shown in the figure. The material is placed inside a long solenoid which contains 1000 turns/cm. The current that should be passed in the solenoid to demagnetize the ferromagnet completely is _____.

(a)

1.00 m A

(b)

1.25 mA

(c)

1.50 mA

(d)

1.75 mA

13.

A circular coil of radius 5 cm and 50 turns carries a current of 3 ampere. The magnetic dipole moment of the coil is nearly ____.

(a)

1.0 A m²

(b)

1.2 A m²

(c)

0.5 A m²

(d)

0.8 A m²

14.

\(\frac{20}{\pi^2}H\) inductor is connected to a capacitor of capacitance C. The value of C in order to impart maximum power at 50 Hz is

(a)

50 μF

(b)

0.5 μF

(c)

500 μF

(d)

5 μF

15.

An inductor 20 mH, a capacitor 50 μF and a resistor 40Ω are connected in series across a source of emf V = 10 sin 340 t. The power loss in AC circuit is

(a)

0.76 W

(b)

0.89 W

(c)

0.46 W

(d)

0.67 W

16.

In an electrical circuit, R, L, C, and AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and current in the circuit is \(\frac{\pi}{3}\). Instead, if C is removed from the circuit, the phase difference is again \(\frac{\pi}{3}\). The power factor of the circuit is

(a)

1/2

(b)

1/\(\sqrt2\)

(c)

(d)

\(\sqrt3\)/2

17.

The current i flowing in a coil varies with time as shown in the figure. The variation of induced emf with time would be

(a)

(b)

(c)

(d)

18.

If E = E_o sin[10⁶ x -ωt] be the electric field of a plane electromagnetic wave, the value of ω is_____.

(a)

0.3 x 10⁻¹⁴ rad s⁻¹

(b)

3 x 10⁻¹⁴ rad s⁻¹

(c)

0.3 x 10¹⁴ rad s⁻¹

(d)

3 x 10¹⁴ rad s^-1

19.

During the propagation of electromagnetic waves in a medium __________________.

(a)

electric energy density is double of the magnetic energy density

(b)

electric energy density is half of the magnetic energy density

(c)

electric energy density is equal to the magnetic energy density

(d)

both electric and magnetic energy densities are zero

20.

Which of the following electromagnetic radiations is used for viewing objects through fog

(a)

microwave

(b)

gamma rays

(c)

X- rays

(d)

infrared

21.

Two metallic spheres of radii 1 cm and 3 cm are given charges of -1 \(\times\) 10^-2 C and 5 \(\times\) 10^-2 C respectively. If these are connected by a conducting wire, the final charge on the bigger sphere is

(a)

3 \(\times\) 10^-2 C

(b)

4 \(\times\) 10^-2 C

(c)

1 \(\times\) 10^-2 C

(d)

2 \(\times\) 10^-2 C

22.

If voltage applied on a capacitor is increased from V to 2V, choose the correct conclusion.

(a)

Q remains the same, C is doubled

(b)

Q is doubled, C doubled

(c)

C remains same, Q doubled

(d)

Both Q and C remain same

23.

The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Ω is ______.

(a)

0.2 Ω

(b)

0.5 Ω

(c)

0.8 Ω

(d)

1.0 Ω

24.

Two wires of A and B with circular cross section made up of the same material with equal lengths. Suppose R_A = 3 R_B, then what is the ratio of radius of wire A to that of B?

(a)

(b)

\(\sqrt3\)

(c)

\(\frac{1}{\sqrt3}\)

(d)

\(\frac{1}{3}\)

25.

A carbon resistor of (47 ± 4.7 ) k Ω to be marked with rings of different colours for its identification. The colour code sequence will be ______.

(a)

Yellow – Green – Violet – Gold

(b)

Yellow – Violet – Orange – Silver

(c)

Violet – Yellow – Orange – Silver

(d)

Green – Orange – Violet - Gold

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Answers Key:

Multiple Choice Question

25 x 1 = 25

Parrot fish's source of bite → mimic → Ultra durable synthetic material.
Lotus leaf surface → SEM → Self Cleaning Process
The scales on the wings of a morpho butterfly → mimic → Interaction of colours.
Peacock feathers → mimic → Glowing in different colours.

(b)
Frequency modulation

\(Y_1=\overline{A+B}, y_2=\overline{A+B}=A+B, y=\overline{A+B}\)

(d)
A closed switch in series with a small resistance and a battery

\(\frac{BE}{A}=\frac{\Delta\times931MeV}{V}=\frac{0.042 \times931}{7}\)
= 5.586 = 5.6 MeV

(b)
1.7 × 10¹¹ Ckg^–1

\(K .E_{\max } =\mathrm{hv}-\phi \)
\(=\frac{\mathrm{hc}}{\lambda}-\phi \)
\(\mathrm{E} =\frac{6.6 \times 10^{-34} \times 3 \times 10^8-1.235}{500 \times 10^{-9} \times 1.6 \times 10^{-19}} \)
\(=2.475-1.235 \)
\(\text {K. } \mathrm{E}_{\max } =1.24 \mathrm{eV}\)

\(\lambda_{\mathrm{i}} \frac{1}{\mathrm{mv}} \)
\(\frac{\lambda_p}{\lambda_e} =\frac{m_e v_e}{m_P v_P} \)
\(1 =\frac{9.1 \times 10^{-31} \times 6 \times 10^6}{3 \times 10^{-9} \times v_p} \)
\(\mathrm{v}_{\mathrm{p}} =9.1 \times 10^{-16} \times 2 \)
\(\mathrm{v}_{\mathrm{p}} =18.2 \times 10^{-16} \)
\(\mathrm{v}_{\mathrm{p}} =1.82 \times 10^{-15} \mathrm{~m} \mathrm{~s}^{-1}\)

Refractive index for violet is more and wavelength for violet is very low comparing other colours. So, the letter which appears to be raised more is violet.

10.

(a)
30^o

11.

12.

13.

Dipole moment, \(\vec{p}_m=n\times I\times\vec{A}\)
\(\vec{p}_m\) = 50 x 3 x 3.14 x 25 x 10^-4 ≈ 1.2 A m²

14.

\(L=\frac{20}{\pi^2} \mathrm{H}, \mathrm{f}=50 \mathrm{~Hz} \)
\(f=\frac{1}{2 \pi \sqrt{L C}} \)
\(50=\frac{1}{2 \pi \sqrt{\frac{20}{\pi^2} \times C}} \)
\(50=\frac{1}{2 \times \sqrt{20 C}} \)
\(\therefore(50)^2=\frac{1}{4 \times 20 C} \)
\(\therefore C=\frac{1}{2500 \times 4 \times 20}=5 \times 10^{-6}=5 \mu \mathrm{F}\)

15.

L = 20 x 10^-3H. C = 50 x 10^-6 F, R= 40Ω
enf V = 10 sin 340 t
\(\therefore V_0=10 \mathrm{~V}, \omega=340 \)
\(X_1=1 \omega^{\prime}=20 \times 10^3 \times 340 \)
\(=6800 \times 10^{-1}=6.8 \Omega \)
\(X_C=\frac{1}{C .} \)
\(=\frac{1}{50 \times 10^{-\alpha} \times 340}=\frac{10^{\circ}}{17000}=\frac{10^{\prime}}{17}=58.823 \Omega \)
\(Z=\sqrt{R^2+\left(X_6-X_1\right)^2} \)
\(=\sqrt{(40)^2+(58.82-6.8)^2} \)
\(=\sqrt{(40)^2+(52.02)^2} \)
\(=65.62 \Omega\)
The peak current in the circuit is,
\(I_0=\frac{V_0}{Z}=\frac{10}{65.62} \)
\(\cos 0=\frac{R}{Z}=\frac{40}{65.62} \)
\(\text{Power loss in A.C. circuit }=V_{r m} 1_{r \rightarrow \infty} \cos \phi \)
\(=\frac{1}{2} V_{\mathrm{o}} I_{\mathrm{c}} \cos \phi \)
\(=\frac{1}{2} \times 10 \times \frac{10}{65.62} \times \frac{40}{65.62}\)
\(\frac{2000}{4305.98}\)
= 0.46 W

16.

\(\Phi = \frac{\pi}{3}-\frac{\pi}{3}=0 \)
Power factor = cosФ = cos 0 = 1

17.

Solution
e = -L\(\frac{dl}{dt}\)

18.

E = E_o sin(kx – ωt)
ω = ck
ω = 3 x 10⁸ x 10⁶
ω = 3 x 10¹⁴ rad s^-1

19.

20.

(d)
infrared

21.

Q = q₁ + q₂ = 4 x 10^-2C
\(q_{2f}=Q[\frac{r_2}{r_1+r_2}]\)
= 4 x 10^-2 \([\frac{3}{4}]\)
q_2f= 3 x 10^-2 C

22.

If voltage is increased from V to 2 V
Then Q₁ = CV
Q₂ = C(2 V) = 2 CV
∴ Q is doubled and C remains same

23.

I = 0.2 A, R = 10 Ω, E = 2.1 V
\(I=\frac{ɛ}{R+r}\)
\(0.2=\frac{2.1}{10+r}\)
0.2 x (10 + r) = 2.1
2 + 0.2 r = 2.1
0.2 r = 2.1 - 2 = 0.1
Internal resistance, \(r=\frac{0.1}{0.2}=\frac{1}{2}\)
r = 0.5 Ω

24.

\(R \propto \frac{1}{A}, R \propto \frac{1}{r^2} \)
\(R_A \propto \frac{1}{r_A^2}, R_B \propto \frac{1}{r_B^2} \)
\(\frac{r_A}{r_B}=\left(\frac{R_B}{R_A}\right)^{1 / 2}=\left(\frac{R_B}{3 R_B}\right)^{1 / 2}=\frac{1}{3^{\frac{1}{2}}}=\frac{1}{\sqrt{3}}\)

25.

Yellow - 4
Violet - 7
Orange - 10³
Silver - Tolerance - 10%