# CBSEtips.in

## Thursday 28 January 2021

### CBSE Class 12 Physics - MCQ and Online Tests - Unit 8 - Electromagnetic Waves

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 8 – Electromagnetic Waves

Every year CBSE conducts board exams for 12th standard. These exams are very competitive to all the students. So our website provides online tests for all the 12th subjects. These tests are also very effective and useful for those who preparing for competitive exams like NEET, JEE, CA etc. It can boost their preparation level and confidence level by attempting these chapter wise online tests.

These online tests are based on latest CBSE Class 12 syllabus. While attempting these our students can identify the weak lessons and continuously practice those lessons for attaining high marks. It also helps to revise the NCERT textbooks thoroughly.

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 8 – Electromagnetic Waves

Question 1.
Maxwell’s equation involving $$\frac{d}{dt}$$ $$\vec{B}$$ is obtained-from:
(a) Ampere’s law
(b) Gauss’s law
(d) Biot-Savart’s law

Question 2.
Which of the following laws was modified by Maxwell by introducing the displacement current?
(a) Gauss’s law
(b) Ampere’s law
(c) Biot-Savart’s law
(d).None of these

Question 3.
The dimensional formula of $$\vec{E}$$ is:
(a)[MLT-2A-1]
(b) [MLT-3A-1]
(c) [MLT-2A-2]
(d) None of these

Question 4.
Electromagnetic waves have a speed of
(a) 3 × 105 kms-1
(b)3 × 106 kms-1
(c) 3 × 107 kms-1
(d) 3 × 108 kms-1

Answer: (a) 3 × 105 kms-1

Question 5.
The dimensions of $$\vec{E}$$, $$\vec{dl}$$ are identical to that of:
(a) potential
(b) charge
(c) current
(d) None of these

Question 6.
Which of the following EMW has highest wavelength?
(a) X-ray
(b) ultraviolet rays
(c) infrared rays
(d) microwaves

Question 7.
The dimensional formula of is:
(a) [MLT-2A-1]
(b) [ML0T-2A-1]
(c) [ML0T-3A-1]
(d) None of these

Question 8.
Displacement current is always :
(a) equal to conduction current
(b) less than conduction current
(c) greater than conduction current
(d) the sum of current due to flow of positive and negative ions

Answer: (a) equal to conduction current

Question 9.
Choose the wave relevant to telecommunication :
(a) ultraviolet
(b) infrared
(c) microwave
(d) visible light

Question 10.
EMW are produced by:
(a) charge in uniform motion only
(b) charge at rest only
(c) accelerated or decelerated charge only
(d) all of the above

Answer: (c) accelerated or decelerated charge only

Question 11.
If $$\vec{B}$$ is the magnetic field vector and $$\vec{E}$$ is the electric field vector in an em wave, then which of the following relations is correct? Here c is the speed of fight:
(a) c = $$\frac{E}{B}$$
(b) c = BE
(c) c = $$\frac{B}{E}$$
(d) c = $$\frac{1}{EB}$$

Answer: (a) c = $$\frac{E}{B}$$

Question 12.
The dimensions of E/Bare same as that of:
(a) charge
(b) current
(c) velocity
(d) acceleration

Question 13.
Name the law which states that a varying electric field produces a magnetic field:
(a) Biot-Savart’s law
(c) Modified Ampere’s law
(d) None of these

Question 14.
The existence of EMW was experimentally established by :
(a) Sir S. C. Bose
(b) Maxwell
(c) Marconi
(d) Hertz

Answer: (a) Sir S. C. Bose

Question 15.
Displacement current is due to:
(a) the flow of electrons
(b) the Varying electric field
(c) the ionization of atmosphere
(d) the flow of protons

Answer: (b) the Varying electric field

Question 16.
Who first demonstrated the existence of em waves?
(a) Hertz
(b) Maxwell
(c) Ampere

Question 17.
Light Year is the unit of:
(a) distance
(b) time
(c) energy
(d) intensity of light

Question 18.
An EMW of v = 3 MHz passes from vacuum into dielectric medium with permittivity Er = 4, then:
(a) Wavelength is doubled and the frequency remains unchanged
(b) Wavelength is doubled and the frequency become half
(c) Wavelength is halved and the frequency remains unchanged
(d) Wavelength and frequency both remain unchanged

Answer: (c) Wavelength is halved and the frequency remains unchanged

Question 19.
Frequency of a wave is 6 × 1015. Hz. The wave is :
(b) Microwave
(c) X-ray
(d) Ultra violet

Question 20.
If ue and um arc the electric and magnetic field densities in an electromagnetic wave, then (c is the speed of light):
(a) ue = um
(b) ue = c um
(c) ue = $$\frac{u_m}{c}$$
(d) None of these

Question 21.
(a) transverse EMW
(b) longitudinal EMW
(c) both (a) and (b)
(d) None of these

Question 22.
Choose the wrong statement?
(a) Electromagnetic waves are transverse
(b) Electromagnetic waves travel with the speed of light in free space
(c) Electromagnetic waves are produced by accelerating charges
(d) Electromagnetic waves travel with the same speed in all media

Answer: (d) Electromagnetic waves travel with the same speed in all media

Question 23.
Which of the following has the dimensions of current?
(a) ε0 $$\vec{E}$$.$$\vec{dt}$$
(b) µ0 $$\vec{E}$$.$$\vec{dt}$$
(c) $$\frac{\vec{B}.\vec{dl}}{µ_0}$$
(d) $$\frac{\vec{B}.\vec{dl}}{ε_0}$$

Answer: (c) $$\frac{\vec{B}.\vec{dl}}{µ_0}$$

Question 24.
Which of the following has the dimensions of charge?
(a) $$\frac{ε_0\vec{E}}{\vec{ds}}$$
(b) µ0 $$\vec{E}$$.$$\vec{ds}$$
(c) $$\frac{ε_0}{µ_0}$$ $$\vec{E}$$.$$\vec{ds}$$
(d) $$\frac{µ_0}{ε_0}$$ $$\vec{E}$$.$$\vec{ds}$$

Answer: (a) $$\frac{ε_0\vec{E}}{\vec{ds}}$$

Question 25.
Ampere’s circuital law was modified by:
(a) Laplace
(b) Gauss
(c) Maxwell
(d) Hertz

Share: