Question Set C

TN 12th Standard Physics Current Electricity Creative Questions Study Material - QB365

Download Tamil Nadu 12th Standard Physics question papers, model tests, one-mark questions, important questions, and public exam papers in PDF format. Free study materials and answer keys for TN State Board students.

Questions:

Multiple Choice Question

30 x 1 = 30

An e.m. wave is propagating in a medium with a velocity \(\vec{v}=v \hat{i}\). The instantaneous oscillating electric field of this e.m. wave is along + y-axis, then the direction of oscillating magnetic field of the e.m. wave will be along _____.

(a)

–y direction

(b)

–x direction

(c)

+z direction

(d)

–z direction

The barrier potential of a p-n junction depends on
i) type of semiconductor material
ii) amount of doping
iii) temperature. Which one of the following is correct?

(a)

(i) and (ii) only

(b)

(ii) only

(c)

(ii) and (iii) only

(d)

(i) (ii) and (iii)

To calculate magnetic induction due to a current carrying conductor ________________law is utilised.

(a)

Gauss

(b)

Ampere

(c)

Kirchhoff's

(d)

Biot-Savart

Resistance of a metal wire of length 10 cm is \(2 \Omega\). If the wire is stretched uniformly to 50 cm the resistance is______________.

(a)

\(10 \Omega\)

(b)

\(50 \Omega\)

(c)

\(5 \Omega\)

(d)

\(25 \Omega\)

______ theory explains photo electric effect.

(a)

Electromagnetic

(b)

Quantum

(c)

Wave

(d)

Corpuscular

The minimum potential given to the anode for which the photoelectric current becomes zero is called _______ potential.

(a)

cut-off

(b)

threshold

(c)

saturation

(d)

active

A common - emitter amplifier has a voltage gain of 100, an input impendence of 100Ω and an output impedence of 200 Ω. The product of voltage gain and current gain is _________

(a)

1000

(b)

3000

(c)

5000

(d)

500

If γ is the frequency of characteristic X-ray line emitted by a target element of atomic number Z, then Moseley's law is __________________.

(a)

γ α Z

(b)

γ α \(\sqrt Z\)

(c)

γ α Z²

(d)

γ α Z³

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

(a)

Lotus leaf

(b)

Morpho butterfly

(c)

Parrot fish

(d)

Peacock feather

10.

Which one of the following represents forward bias diode?

(a)

(b)

(c)

(d)

11.

If a positive half-wave rectified voltage is fed to a load resistor, for which part of a cycle there will be current flow through the load?

(a)

0⁰–90⁰

(b)

90⁰–180⁰

(c)

0⁰–180⁰

(d)

0⁰–360⁰

12.

The half-life period of a radioactive element A is same as the mean life time of another radioactive element B. Initially both have the same number of atoms. Then _____.

(a)

A and B have the same decay rate initially

(b)

A and B decay at the same rate always

(c)

B will decay at faster rate than A

(d)

A will decay at faster rate than B

13.

In a hydrogen atom, the electron revolving in the fourth orbit, has angular momentum equal to _____.

(a)

(b)

\(\frac{h}{\pi}\)

(c)

\(\frac{4h}{\pi}\)

(d)

\(\frac{2h}{\pi}\)

14.

The work functions for metals A, B and C are 1.92 eV, 2.0 eV and 5.0 eV respectively. The metal/metals which will emit photoelectrons for a radiation of wavelength 4100 Å is/are _____.

(a)

A only

(b)

both A and B

(c)

all these metals

(d)

none

15.

In an electron microscope, the electrons are accelerated by a voltage of 14 kV. If the voltage is changed to 224 kV, then the de Broglie wavelength associated with the electrons would _____.

(a)

increase by 2 times

(b)

decrease by 2 times

(c)

decrease by 4 times

(d)

increase by 4 times

16.

Light transmitted by Nicol prism is, _____.

(a)

partially polarised

(b)

unpolarised

(c)

plane polarised

(d)

elliptically polarised

17.

Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm approximately. The maximum distance at which these dots can be resolved by the eye is_____. [take wavelength of light, λ = 500 nm]

(a)

1 m

(b)

5 m

(c)

3 m

(d)

6 m

18.

A ray of light travelling in a transparent medium of refractive index n falls, on a surface separating the medium from air at an angle of incidents of 45^o . The ray can undergo total internal reflection for the following n, ______.

(a)

n = 1.25

(b)

n = 1.33

(c)

n = 1.4

(d)

n = 1.5

19.

A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is, ______.

(a)

2.5 cm

(b)

5cm

(c)

10 cm

(d)

15cm

20.

The power factor of an a.c, circuit is _________

(a)

\(\phi \)sin\(\phi \)

(b)

cosec \(\phi \)

(c)

cos \(\phi \)

(d)

tan \(\phi \)

21.

If C is the capacitance of an air filled capacitor and C is the capacitance of dielectric filled capacitor, then

(a)

C'ε_rC'

(b)

\(C'=\frac { C }{ { \varepsilon }_{ r } } \)

(c)

\(C'=\frac { { \varepsilon }_{ r } }{ C } \)

(d)

\(C'={ \varepsilon }_{ 0 }{ \varepsilon }_{ r }\)

22.

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

23.

An electron moves in a straight line inside a charged parallel plate capacitor of uniform charge density σ. The time taken by the electron to cross the parallel plate capacitor undeflected when the plates of the capacitor are kept under constant magnetic field of induction \((\vec{B})\) is

(a)

\({ \varepsilon }_{ ° }\frac { elB }{ \sigma } \)

(b)

\({ \varepsilon }_{ ° }\frac { lB }{ \sigma {l} } \)

(c)

\({ \varepsilon }_{ ° }\frac { lB }{ {e}\sigma } \)

(d)

\({ \varepsilon }_{ ° }\frac { lB }{ \sigma } \)

24.

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

25.

A thin semi-circular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure.

The potential difference developed across the ring when its speed v, is

(a)

Zero

(b)

\(\frac { { Bv\pi { r }^{ 2 } } }{ 2 } \) and P is at higher potential

(c)

πrBv and R is at higher potential

(d)

2rBv and R is at higher potential

26.

If the amplitude of the magnetic field is 3 x 10⁻⁶ T, then amplitude of the electric field for a electromagnetic waves is _____.

(a)

100 V m⁻¹

(b)

300 V m^-1

(c)

600 V m^-1

(d)

900 V m^-1

27.

Rank the electrostatic potential energies for the given system of charges in increasing order

(a)

1 = 4 < 2 < 3

(b)

2 = 4 < 3 < 1

(c)

2 = 3 < 1 < 4

(d)

3 < 1 < 2 < 4

28.

Which charge configuration produces a uniform electric field?

(a)

point charge

(b)

uniformly charged infinite line

(c)

uniformly charged infinite plane

(d)

uniformly charged spherical shell

29.

The temperature coefficient of resistance of a wire is 0.00125 per °C. At 20°C, its resistance is 1 Ω. The resistance of the wire will be 2 Ω at ______.

(a)

800 °C

(b)

700 °C

(c)

850 °C

(d)

820 °C

30.

A wire of resistance 2 ohms per meter is bent to form a circle of radius 1m. The equivalent resistance between its two diametrically opposite points, A and B as shown in the figure is

(a)

\(\pi \Omega\)

(b)

\(\frac{\pi}{2}\Omega\)

(c)

2\(\pi \Omega\)

(d)

\(\frac{\pi}{4}\Omega\)

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Answers Key:

Multiple Choice Question

30 x 1 = 30

(d)
(i) (ii) and (iii)

(d)
Biot-Savart

\(R_n=n^2 R_1=(5)^2 \times 2=50 \Omega\)

(b)
Quantum

(a)
cut-off

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.

10.

11.

12.

T_A1/2 = ፒ_B
\(\frac{0.6931}{\lambda_{\mathrm{A}}}=\frac{1}{\lambda_{\mathrm{B}}} \)
\(\lambda_{\mathrm{B}}=\frac{\lambda_{\mathrm{A}}}{0.6931}=1.44 \lambda_{\mathrm{A}}\)
Hence, B will decay at faster rate than A

13.

\(L=\frac{nh}{2\pi}=\frac{4h}{2\pi}=\frac{2h}{\pi}\)

14.

\(E=\frac{12400 \stackrel{o}A}{4100 \stackrel{o}A}=3.02 eV\)

15.

\(\lambda\propto \frac{1}{\sqrt{V}}\)
\(\frac{\lambda_1}{\lambda_2}=\frac{\sqrt{224\times10^3}}{\sqrt{14\times 10^3}}\)
\(=\sqrt{16}=4\)
\(\lambda_{\mathrm{2}}= \frac{\lambda_1}{4}\)

16.

17.

λ = 500 nm = 500 x 10^-9 m
x = 3 mm = 3 x 10^-3 m
a = 1 mm = 1 x 10^-3 m
\(d=\frac{xa}{1.22 \lambda}\)
\(d=\frac{3 \times1\times10^{-6}}{1.22 \times500\times10^{-9}}\)
\(=\frac{3 \times1\times10^{-6}}{6.10 \times 10^{-7}}\)
\(d=\frac{30}{6.1}=5 m\)

18.

For total internal reflection,
sin i > sin c
\(n=\frac{1}{sin \ c}\)
\(sin \ c=\frac{1}{n}\)
\(sin \ i>\frac{1}{n}\)
\(n>\frac{1}{sin \ i}\)
n >\(\sqrt{2}\)
n >1.414 = 1.5

19.

At end A,
\(\frac{1}{f} =\frac{1}{u_A}+\frac{1}{v_A} \)
\(\therefore \frac{1}{v_A} =\frac{1}{-10}-\frac{1}{-20} \)
\(\frac{1}{v_A} =-\frac{1}{10}+\frac{1}{20}=\frac{-2+1}{20}=-\frac{1}{20} \)
\(v_A =-20 \mathrm{~cm} \)
\(\left|v_{\wedge}\right|=20 \mathrm{~cm}\)
At end B,
\(\frac{1}{f} =\frac{1}{u_B}+\frac{1}{v_B} \)
\(\frac{1}{v_B} =\frac{1}{f}-\frac{1}{u_B}, \)
\(u_B =-30 \mathrm{~cm} \)
\(\frac{1}{v_B} =-\frac{1}{10}+\frac{1}{30} \)
\(=\frac{-3+1}{30}=\frac{-2}{30}=\frac{-1}{15} \)
\(v_B =-15 \mathrm{~cm} \)
\(\left|v_B\right| =15 \mathrm{~cm} \)
\(\therefore \quad\left|\mathrm{v}_{\mathrm{A}}\right|-\left|\mathrm{v}_{\mathrm{B}}\right| \) is the length of the image
= 20 - 15 = 5 cm

20.

21.

(a)
C'ε_rC'

22.

23.

Electric field between the plates \(= \frac{σ}{ε_0}\)
Electric force on an electron \(= e\frac{σ}{ε_0}\)
Magnetic force on an electron, F = BIl
But, \(I= \frac{e}{t}\)
∵Electron moves in a straight line. So,
E_F= M_F
\(e\frac{σ}{ε_0}=B(\frac{e}{t})l\)
\(\therefore t = ε_0\frac{lB}{σ}\)

24.

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

25.

(d)
2rBv and R is at higher potential

26.

B_o = 3 x 10^-6T
Amplitude of electric field, E_o = B_oc
E_o= 3 x 10^-6x 3 x 10⁸ = 900V m ^-1

27.

\(U=\frac{1}{4\piε_0}\frac{q_1q_2}{r_{12}}\)
\(i) U=\frac{1}{4\piε_0}\frac{Q(-Q)}{r}=\frac{1}{4\piε_0}[\frac{-Q^2}{r}]\)
\(ii) U=\frac{1}{4\piε_0}\frac{(-Q)(-Q)}{r}=\frac{1}{4\piε_0}[\frac{Q^2}{r}]\)
\(iii) U=\frac{1}{4\piε_0}\frac{Q(2Q)}{r}=\frac{1}{4\piε_0}[\frac{2Q^2}{r}]\)
\(iv) U=\frac{1}{4\piε_0}\frac{Q(-2Q)}{2r}=\frac{1}{4\piε_0}[\frac{-Q^2}{r}]\)
From the values, 1 = 4 < 2 < 3

28.

29.

R_t = R_o [1 + α(T₂ - T₁)
2 = 1[1 + 0.00125(T₂ - 293)
I = 5/4 x 10^-3(T₂ - 293)
T₂ = 1093 K
T₂ = 820 ^oC