Karnataka Board PUCPUC Science 2nd PUC Class 12

A Wire Carries an Alternating Current I = I0 Sin ωT. is There an Electric Field in the Vicinity of the Wire? - Physics

Short Note

A wire carries an alternating current i = i0 sin ωt. Is there an electric field in the vicinity of the wire?



When an alternating current passes through a conductor, the changing magnetic field create a changing electric field outside it. An electromagnetic field is radiated from the surface of the conductor. There is a time-varying electric field outside the conductor. Hence, there is a time-varying electric field in the vicinity of the wire.

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Chapter 18: Electromagnetic Waves - Short Answers [Page 338]


HC Verma Class 11, Class 12 Concepts of Physics Vol. 2
Chapter 18 Electromagnetic Waves
Short Answers | Q 4 | Page 338

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Write mathematical expressions for electric and magnetic fields of an electromagnetic wave propagating along the z-axis.

How is the speed of em-waves in vacuum determined by the electric and magnetic field?

In the study of a photoelectric effect the graph between the stopping potential V and frequency v of the incident radiation on two different metals P and Q is shown below:

(i) Which one of the two metals has higher threshold frequency?

(ii) Determine the work function of the metal which has greater value.

(iii) Find the maximum kinetic energy of electron emitted by light of frequency 8 × 1014 Hz for this metal.

Do electromagnetic waves carry energy and momentum ?

Identify the electromagnetic waves whose wavelengths vary as:

(a) 10–12 m < λ < 10–8 m

(b) 10–3 m < λ < 10–1 m

Write one use for each.

What is the ratio of the speed of gamma rays to that of radio waves in a vacuum?

How are electric vector `(vec "E")`, magnetic vector `(vec "B")` and velocity vector `(vec "C")` oriented in an electromagnetic wave?

Write the expression for speed of electromagnetic waves in a medium of electrical permittivity ε and magnetic permeability μ.

Which em waves lie near the high frequency end of visible part of em spectrum? Give its one use. In what way this component of light has harmful effects on humans?

Arrange the following electromagnetic waves in decreasing order of wavelength:

γ-rays, infrared rays, X-rays and microwaves.

Write the following radiations in ascending order with respect to their frequencies:

X-rays, microwaves, UV rays and radio waves.

Can an electromagnetic wave be deflected by an electric field or a magnetic field?

A capacitor is connected to an alternating-current source. Is there a magnetic field between the plates?

Can an electromagnetic wave be polarised?

A plane electromagnetic wave is passing through a region. Consider (a) electric field (b) magnetic field (c) electrical energy in a small volume and (d) magnetic energy in a small volume. Construct the pairs of the quantities that oscillate with equal frequencies.

An electromagnetic wave going through vacuum is described by
E = E0 sin (kx − ωt); B = B0 sin (kx − ωt).
Which of the following equations is true?

Which of the following have zero average value in a plane electromagnetic wave?
(a) Electric field
(b) Magnetic field
(c) Electric energy
(d) Magnetic energy

The energy associated with light of which of the following colours is minimum : 

This is an example of step-up transformer .

Define frequency modulation and state any one advantage of frequency modulation (FM) over amplitude modulation (AM). 

State any one property which is common to all electromagnetic waves.

The energy levels of an atom of a certain element are shown in the given figure. Which one of the transitions A, B, C, D or E will result in the emission of photons of electromagnetic radiation of wavelength 618.75 nm? Support your answer with mathematical calculations.

How are electromagnetic waves produced? What is the source of the energy carried by a propagating electromagnetic wave?
Identify the electromagnetic radiations used
(i) In remote switches of a household electronic device; and
(ii) as a diagnostic tool in medicine

The dimension of `1/(mu_0 ∈_0)` is

Consider an oscillator which has a charged particle oscillating about its mean position with a frequency of 300 MHz. The wavelength of electromagnetic waves produced by this oscillator is ______.

Let E = E0 sin[106 x -ωt] be the electric field of plane electromagnetic wave, the value of ω is ______.

What are electromagnetic waves?

Explain the Maxwell’s modification of Ampere’s circuital law.

Write down the properties of electromagnetic waves.

Discuss the source of electromagnetic waves.

A transmitter consists of LC circuit with an inductance of 1 μH and a capacitance of 1 μF. What is the wavelength of the electromagnetic waves it emits?

Let an electromagnetic wave propagate along the x-direction, the magnetic field oscillates at a frequency of 1010 Hz and has an amplitude of 10-5 T, acting along the y – direction. Then, compute the wavelength of the wave. Also write down the expression for the electric field in this case.

If the relative permeability and relative permittivity of the medium is 1.0 and 2.25, respectively. Find the speed of the electromagnetic wave in this medium.

The speed of plane electromagnetic waves is maximum in ______.

A man standing on the road has to hold his umbrella at 30° with the vertical to keep the rain away. He throws away the umbrella and starts, running at 10 km/h and finds raindrops hitting his head vertically. The speed of the raindrops with respect to the road is ______.

In space communication, the sound waves can be sent from one place to another

A plane electromagnetic wave travels in free space along x-axis. At a particular point in space, the electric field along y-axis is 9.3 Vm−1. The magnetic induction (B) along z-axis is:

Dimensions of 1/(µOE0) is

Which of the following electromagnetic radiations has the smallest wave length?

An accelerate electron would produce.

If a source is transmitting electromagnetic waves of frequency 8.2 × 106 Hz. then wavelength of electromagnetic waves transmitted from the source will be.

The velocity of light in vacuum can be changed by changing

Which of the following are not electromagnetic waves?

Dimensions of ε0 `(d phi_ε)/(dt)` are of

Electromagnetic waves are produced by ______.

Which of the following type of radiations are radiated by an oscillating electric charge?

For a plane electromagnetic wave propagating in x-direction, which one of the following combinations gives the correct possible directions for electric field (E) and magnetic field (B) respectively?

For a plane electromagnetic wave propagating in the x-direction, which one of the following combinations gives the correct possible directions for the electric field (E) and magnetic field (B) respectively?

Why is the orientation of the portable radio with respect to broadcasting station important?

A plane EM wave travelling along z direction is described by `E = E_0 sin (kz - ωt)hati` and `B = B_0 sin (kz - ωt)hatj`. show that 

  1. The average energy density of the wave is given by `u_(av) = 1/4 ε_0E_0^2 + 1/4 B_0^2/mu_0`.
  2. The time averaged intensity of the wave is given by `I_(av) = 1/2 cε_0 E_0^2`.

The intensity of the light from a bulb incident on a surface is 0.22 W/m2 . The amplitude of the magnetic field in this light-wave is ______× 10–9 T. 

(Given: Permittivity of vacuum ε0 = 8.85 × 10–12 C2 N–1 – m–2, speed of light in vacuum c = 3 × 108 ms-1)

For an electromagnetic wave travelling in free space, the relation between average energy densities due to electric (Ue) and magnetic (Um) fields is ______.

A plane electromagnetic wave, has frequency of 2.0 × 1010 Hz and its energy density is 1.02 × 10-8 J/m3 in vacuum. The amplitude of the magnetic field of the wave is close to `(1/(4piepsilon_0) = 9xx10^9"Nm"^2/"C"^2  "and speed of light" = 3 xx 10^8  "m"  "s"^-1)`:

A plane electromagnetic wave travels in free space along the x-direction. The electric field component of the wave at a particular point of space and time is E = 6 Vm-1 along the y-direction. Its corresponding magnetic field component, B would be ______.

Sunlight falls normally on a surface of area 36 cm2 and exerts an average force of 7.2 × 10-9 N within a time period of 20 minutes. Considering a case of complete absorption the energy flux of incident light is ______.

The electric field in an electromagnetic wave is given by E = 56.5 sin ω(t - x/c)Nc-1. Find the intensity of the wave if it is propagating along x-axis in the free space.

(Given ε0 = 8.85 × 10-12 C2 N-1 m-2)

A plane electromagnetic wave with frequency of 30 MHz travels in free space. At particular point in space and time, electric field is 6 V/m. The magnetic field at this point will be x × 10-8 T. The value of x is ______.

An electromagnetic wave of frequency 3 GHz enters a dielectric medium of relative electric permittivity 2.25 from vacuum. The wavelength of this wave in that medium will be ______ × 10-2 cm. 

In a plane electromagnetic wave, the direction of electric field and magnetic field are represented by `hat"k"` and 2`hat"i" - 2hat"j"`, respectively. What is the unit vector along direction of propagation of the wave.

An electromagnetic wave of frequency v = 3.0 MHz passes from vacuum into a dielectric medium with permittivity ∈ = 4.0. Then ______.

Name the electromagnetic wave/radiation which is used to study crystal structure.


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