45406 + Interview Questions in Physics in Class 12

1.	In a nuclear fusion reactor, the reaction occurs in two stages (i) Two deuterium (""_(1)^(2)D) nuclei fuse to form a tritium (""_(1)^(3)T) nucleus with a proton as a byproduct. The reaction may be represented as D (D,p) T. (ii) A tritium nucleus fuseswith another deuterium nucleus to form a helium (""_(2)^(4)He) nucleus with a neutron as a byproduct. The reaction is represented as T(D.n)alpha. Given thatm(""_(1)^(2)d)=2.014104u (atom) m(""_(1)^(3)T)=3.01609u (atom) What percentage of the mass energy of the initial deuterium is released?
Answer» `0.184%` `0.284%` `0.384%` `0.484%` ANSWER :D

Discussion

2.	Two resistors with temperature coefficients of resistane alpha_(1) and alpha_(2) have resistances R_(1) and R_(2) at0^(@)C. Find the temperature coefficient of the compound resistor consisting of the two resistors connected in parallel
Answer» `(R_(1)alpha_(1)+R_(2)alpha_(2))/(R_(1)+R_(2))` `(alpha_(1)+alpha_(2))/(2)` `(2alpha_(1)alpha_(2))/(alpha_(1)+alpha_(2))` `(R_(1)alpha_(2) + R_(2)alpha_(1))/(R_(1)+R_(2))` ANSWER :D

Discussion

3.	In a nuclear fusion reactor, the reaction occurs in two stages (i) Two deuterium (""_(1)^(2)D) nuclei fuse to form a tritium (""_(1)^(3)T) nucleus with a proton as a byproduct. The reaction may be represented as D (D,p) T. (ii) A tritium nucleus fuseswith another deuterium nucleus to form a helium (""_(2)^(4)He) nucleus with a neutron as a byproduct. The reaction is represented as T(D.n)alpha. Given thatm(""_(1)^(2)d)=2.014104u (atom) m(""_(1)^(3)T)=3.01609u (atom) The energy released in 1st stage of fusion reaction is
Answer» 4.033 MeV 17.587 MeV 40.33 MeV 1.7587 MeV Answer :A

Discussion

4.	Find the number density of impurity atoms that must be added to a pure silicon crystal inorder to convert it to have resistivity (i) 10^(-1) Omegam n-type silicon (ii) 10^(-1)Omegam p-type silicon. Give for silicon: mu_(e)=0.135m^(2)V^(-1)s^(-1) and mu_(h)=0.048m^(2)V^(-1)s^(-1).
Answer» Solution :(i)Density of acceptor atoms in P-type SI `N_(d)=(sigma)/(emu_(2))=(1)/(emu_(erho))=(1)/(1.6xx10^(-19)xx0.13xx10^(-1))`

Discussion

5.	Two identical flutes produces fundamental nodes of frequency 300 Hz at 27°C. If the temperature of air in one flute is increases to 31°C the number of the beats per second will be (approx)
Answer» ANSWER :2

Discussion

6.	The path difference for destructive interference is.....
Answer» `n LAMBDA` `((n+1)lambda)/(2)` `n (lambda+1)` `((2n+1)lambda)/(2)` SOLUTION :FORMULA for path difference of DESTRUCTIVE INTERFERENCE `((2n+1) lambda)/(2)` where n=0,1,2,3...)

Discussion

7.	Statement-I : Soft and hard X–rays differ in frequency. Statement-II : Hard X-rays propagate at higher speed than soft X-rays.
Answer» If both Statement- I and Statement- II are TRUE, and Statement - II is the correct explanation of Statement– I. If both Statement - I and Statement-II are true but Statement - II is not the correct explanation of Statement – I. If Statement-I is true but Statement-II is FALSE. If Statement-I is false but Statement-II is true. Answer :C

Discussion

8.	Photoelectric current still continues when the anode is even at a slight negative potential with respect to the photo cathode. Explain.
Answer» Solution :Emitted photoelectrons possess some initial kinetic energy. Hence, a few electrons can reach the anode OVERCOMING the REPULSIVE force of the negative potential. If the value of the negative potential is not too high, photoelectric current CONTINUES to FLOW.

Discussion

9.	In a negative feedback amplifier, the gain without feedback is 100, feed back ratio is 1/25 and input voltage is 50 mV. Calculate feedback voltage
Answer» SOLUTION :feedback VOLTAGE` betaV_0= (1)/(25)XX 1 = 0.04` VOLT

Discussion

10.	In a negative feedback amplifier, the gain without feedback is 100, feed back ratio is 1/25 and input voltage is 50 mV. Calculate feedback factor
Answer» SOLUTION :`BETA =(1)/(25)`

Discussion

11.	In a negative feedback amplifier, the gain without feedback is 100, feed back ratio is 1/25 and input voltage is 50 mV. Calculate output voltage
Answer» SOLUTION :output voltage ` V_0= A_f V_s = 20 xx 50 m V= 1 ` VOLT

Discussion

12.	In a negative feedback amplifier, the gain without feedback is 100, feed back ratio is 1/25 and input voltage is 50 mV. Calculate gain with feedback
Answer» SOLUTION :GAIN with FEEDBACK `A_f= (A )/( 1 +beta A ) = (100 )/(1 + 1//25 xx 100 ) = 20`

Discussion

13.	What is the moment of inertia of a thin rod of length L and mass M about an axis passing through one end and perpendicular to its length?
Answer» `(1)/(3)ML^(2)` `(1)/(12)ML^(2)` `ML^(2)` `(1)/(2)ML^(2)` Solution :Moment of INERTIA of a rod about an axis PASSING through ONE end and `_\|_` to its length is `I=(1)/(3)ML^(2)`.

Discussion

14.	The audio signal cannot be transmitted directly to space. Why?
Answer» Solution :(i) The length of the antenna required is so large(=500m) and it is practically impossible to set it. (ii) The energy daviated from the antenna in audio freqnecy RANGE is practically zero. (iii) The audio DIGNALS TRANSMITTED from the DIFFERENT broadcasting stations will get separately mixed up.

Discussion

15.	What was Think Tank's view about the earthlings at last?
Answer» That Earthlings are planning to ATTACK on the Mars They are more ADVANCED and know techniques of mining and agriculture Both A and B None of the above Answer :C

Discussion

16.	In the cirucit (figure6.3) resistance R_(1) and R_(2) are known and cells ar of emf e_(1) and e_(2) and negligible internal resistance. At what valueof R will the thermal power generated in it be the highest? What is it equal to?
Answer» <P> ANSWER :`R=R_(1)//R_(2//)(R_(1)+R_(2));p_(max)=(epsilon_(1)R_(2)+epsilon_(2)R_(1))/(4R_(1)+R_(2)(R_(1)+R_(2)))`

Discussion

17.	A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10^(-12)F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6?
Answer» Solution :Capacitance of capacitor with air as MEDIUM between the plates , `C_(0)=(in_(0)A)/(d)` `8 xx10^(-12)= (in_(0)A)/(d)` Now, dielectric fHled between two plates of capacitor and the distance between the PLATE is REDUCED to half, then the capacitance will be, `C = (in_(0)A)/((d)/(2)) = (2K in_(0)A)/(d)` `:. C= 2 xx6xx8xx10^(-12) ` ( From equation (1)) `=96 xx10^(-12) F ` `:.C = 96p E `

Discussion

18.	A long copper tube of inner radius R carries a current I. The magnetie field B inside the tube is
Answer» `[(mu_0/2piR) I]` `[(mu_0/4piR) I]` `[(mu_0/2R) I]` zero Answer :D

Discussion

19.	Earthquakes generate sound waves inside the earth.Unlike a gas, theearth can experience both transverse (S) and longitudinal ( P ) sound waves.Typically the speed of S waveis about 4.0 km s^(-1) .and that of P is 8.0 km s^(-1) .Aseismograph records P and S waves from an earthquake.The first P wavearrives 4 min before the first wave.Assuming the waves travel in straight line, at what distance does the earthquake occur ?
Answer» Solution :Let`v_(1),v_(2)` be the VELOCITY of S WAVES & P waves &`t_(1),t_(2)` be the time TAKEN by these waves to travel to the position ofseismograph . If l is the distanceof occurrence of earthquake from the seismograph , then `l= v_(1)t_(1) = v_(2)t_(2)`...(i) now `v_(1) = 4km //s `& ` v_(2)= 8 km//s ` `:. 4t_(1) = 8 t_(2) ` (or) ` t_(1) = 2 t_(2)`...(II) Also `t_(1) - t_(2) = `4 min = 240s using (ii) `, 2t_(2) - t_(2) =240s, t_(2)= 240s ` `t_(1)=2t_(2)=2 xx 240 = 480 s` Now from (i) `l= v_(1) t_(1) = 4 xx 480 = 1920 km` Hence earthquake occurs1920 km away from theseismograph.

Discussion

20.	In a transistor configuration, p parameter is:
Answer» `I_B/I_C` `I_C/I_B` `I_C/I_A` `I_A/I_C` ANSWER :A

Discussion

21.	Which of the following atoms has permanent electric dipole moment zero ?
Answer» HCL `H_(2)O` `NO_(2)` `H_(2)` ANSWER :B

Discussion

22.	Ozone layer blocks the radiation of wavelength
Answer» LESS than `3XX10^(-7)` m equal to `3xx10^(-7)` m more than `3xx10^(-7)` m none of these Solution :OZONE layer blocks ultraviolet radiation from the sun for this radiation `lambda3xx10^(-7) m`

Discussion

23.	(A):Displacement of a body may be zero when distance travelled by it Is not zero. (R ):The displacement is the longest distance between initial and final positions.
Answer» Both (A) and(R ) are true and ( R) is the CORRECT explanation of (A ) Both (A) and (R ) are true and (R ) is not the correct explanation of (A) (A) is true (R )is FALSE Both (A ) and (R ) are false Answer :C

Discussion

24.	At t=0, an inductor of zero resistance is joined to a cell of emfepsi through a resistance. The current increases with a time constant tau . After what time will the potential difference across the coil be equal to that across the resistance ?
Answer» Solution :`V_L = V_R` `E^((Rt)/(L)) = E (1- e^((Rt)/(L)))` ` rArr 2E^(-(Rt)/(L)) = 1 , e^(-R/L t) = 1/2 , e^(R/L t) = 2` ` (Rt)/(L)= LN 2(or )t = L/R ln 2`

Discussion

25.	A ray of light is incident on a rectangular plate at an angle of incidence 60^(@). The light ray suffers a deviation which is 25% of the angle of incidence. The refractive index of the glass will be
Answer» `SQRT(3)` `sqrt(2)` `sqrt(3//2)` `1.5 Answer :C

Discussion

26.	A positively charged ring is in y - z plane with its centre at origin . A positive test charge q_(e ) , held at origin is released along x axis, then its speed
Answer» INCREASES CONTINUOUSLY DECREASES continuously FIRST increases then decreases first decreases then increases Answer :A

Discussion

27.	What is an alpha-particle ? state it's characteristics ?
Answer» SOLUTION :`alpha-particle` is `"_2He^4`. So it has in proton number = 2 and it has in NUCLEON number = 4.

Discussion

28.	A hollow equilateral air prism is immersed in water. Calculate the deviation of a ray incident at an angle 30^(@) from the base side (.^(a)mu_(w)=(4)/(3))
Answer» `8.5^(@)` `12.5^(@)` `16.5^(@)` `20.2^(@)` Solution :(C ) `(sin30^(@))/(sinr)=(mu_(2))/(mu_(1))or(4)/(3)sin30^(@)=1xxsinr` `therefore r = 41.8^(@)` Ray is incident on the adjacent FACE at `18.2^(@)` from the rafracting EDGE. `1.sin18.2=(4)/(3)sine"" [therefore(mu_(a))/(mu_(w))=(sine)/(sin182)]` `therefore e = 13.5^(@)` `D = (41.8^(@) - 30) + (18.2^(@) - 13.5^(@))`

Discussion

29.	If momentum /(p), area a and time (t) are taken to be the fundamental quantities then the energy has the dimensional formula:
Answer» <P>`[p^(1)a^(-1)t^(1)]` `[p^(0)a^(1)t^(1)]` `[p^(1)a^(-1/2)t^(1)]` `[p^(1)a^(1/2)t^(-1)]` Solution :Here `p^(1)=MLT^(-1)` `:.M=(p^(1))/(L^(1)T^(-1))` ALSO `a^(1)=L^(2)` or `L=a^(1//2)` `:.` Energy `=ML^(2)T^(-2)` `=(P^(1))/(L^(1)T^(-1))xxaxxT^(-2)` `(P^(1)xxaxxT^(-2))/(a^(1//2)T^(-1))` `=p^(1)a^(1/2)T^(-1)` `:.(d)` is CORRECT.

Discussion

30.	The de Broglie wavelength of an electron is 1A^(@). In what potential difference electron accelerates
Answer» 100 V 150 225 V 256 V Answer :B

Discussion

31.	A liquid risestoa height of 9 cm in a glass liquid column in a glass capillary of radius 0.03 cm is
Answer» `13.5` cm 9 cm 6 cm 12 cm Solution :`h_(1)r_(1)=h_(2)r_(2)`

Discussion

32.	As soon as current is switched on in a high voltage wire, the bird sitting on it flies away why ?
Answer» Solution :As SOON as CURRENT is switched on, induced current flows through the BODY of the bird of the SINCE CURRENTS through

Discussion

33.	State the types of degrees of freedom of non-rigid diatomic molecules.
Answer» Solution :A soft or non-rigid diatomic molecules has three translational degrees of FREEDOM, two rotational degrees of freedom and ONE VIBRATIONAL DEGREE of freedom. Notes : Rigid diatomic molecules do not have the vibrational degree of freedom.

Discussion

34.	Two rods of equal length and diameter but of thermal conductivities 1.5 and 3 S.I. units respectivity of combination is :
Answer» `2.5` 2 `2.25` `4.5` SOLUTION :In SERIES `k=(2k_(1)k_(2))/(k_(1)+k_(2))=(2xx1.5xx3)/(3+15)=2`. Thus correct choice is (b).

Discussion

35.	If a load of 6 k Omega is used, then the voltage gain of the amplifier is ……… .
Answer» 100 200 300 400 Answer :A

Discussion

36.	What we call the ratio of angle of deviation to change in wavelength ?
Answer» SOLUTION :ANGULAR DISPERSION

Discussion

37.	Radiation or (and ) particles emerge(s) from a radioactive sample. These products from the sample are allowed to pass through a narrow slit and may be considered a beam.The beam is passed between two plates that carry opposite electrical charge. The experiment region contains no magnetic fields. It is observed that the beam is deflected toward the negatively charged plate. Which one of the following statemetns is the best conclusion for this situation?
Answer» The beam is only `alpha` -rays The beam COULD be either `alpha` rays or `BETA^(+)` rays The beam is only `beta^(-)` rays The beam could be `alpha` rays, `beta^(+)` rays, or `gamma` rays Answer :B

Discussion

38.	The ratio of the deBroglie wavelengths of proton, deuteron and alpha particle accelerated through the same potential difference 100V is
Answer» `2:2:1` `1:2:2sqrt2` `2:1:2` `2sqrt2:2:1` ANSWER :D

Discussion

39.	The distance between the plates of a plane capacitor is 10 mm, the voltage is 10 kV. A sheet of mica of the same dimensions as those of the plates is then inserted between the plates. Find the polarization charge on the surface of the mica sheet assuming the plates to remain connected to the power supply.
Answer» Solution : If the plates are CONNECTED to the power supply all the time, the charge on the plates, and CONSEQUENTLY the ELECTRIC field strength, remain constant. The density of the polarization charge is EQUAL to the maritude of the polarization vector of the dielectric: `sigma_("pol")=P=chi_(e)epsi_(0)E-(epsi-1) epsi_(0) varphi//d`

Discussion

40.	A series LR circuit is connected to an ac source of frequency omega and the inductive reactance is equal to 2R. A capacitance of capacitive reactance equal to R is added in series with L and R. The ratio of the new power factor to the old one is
Answer» `SQRT((2)/(3))` `sqrt((2)/(5))` `sqrt((3)/(2))` `sqrt((5)/(2))` Solution :Power factor(OLD) `= (R)/(sqrt(R^(2) + X_(L)^(2))) = (R)/(sqrt(R^(2) + (2R)^(2))) = (R)/(sqrt5R)` Power factor (new) ` = (R)/(sqrt(R^(2) + (X_(L) - X_(C))^(2))) = (R)/(sqrt(R^(2) + (2R - R)^(2))) = (R)/(sqrt 2R)` `therefore` (New power factor)/(Old power factor) = `((R)/(sqrt2R))/((R)/(sqrt5R)) = sqrt((5)/(2))`

Discussion

41.	Two wires of the same material and having the same length but their diameters are in the ratio of 3/2. The ratio of strain energy per unit volume when they are streched will be
Answer» a)`4/9` B)`16/81` C)`9/4` d)`81/16` ANSWER :B

Discussion

42.	Which of the following statements is/are correct? I) a polaroid of long chain molecules aligned in a particular direction II) electric vectors along the direction of the aligned molecules in a polaroid gets absorbed III) an unpolarised light wave is incident on polaroid, then it will get linearly polarized.
Answer» only I both II and III only III only III I, II and III Answer :D

Discussion

43.	Refractive index of lonosphere is
Answer» zero More than one Less than one One Answer :C

Discussion

44.	A microscope consists of two convex lenses of focal lengths 2.0 cm and 6.25 cm placed 15.0 cm apart. Where must the object be placed so that the final virtual image is at a distance of 25 cm from the eye?
Answer» `2.5 CM` `2 cm ` `1.5 cm` `3 cm ` ANSWER :1

Discussion

45.	The ratio of energy of the hydrogen atom in its first and second excited state is:
Answer» `1:4' `4:9' `9:4' `4:1' Answer :C

Discussion

46.	In the Young's double -slit experiment, the interference pattern is found to have intensity ratio between bright and dark fringes as 9.This implies that
Answer» the INTENSITIES at the screen due to the two slits are 5 units and 4 units respectively the intensities at the screen due to the two slits are 1 unit and 4 units respectively the amplitude RATIO is 3 the amplitude ratio is 2 Solution :Here, `((R + 1)/(r -1))^(2) = 9` `RIGHTARROW r = 2` i.e. ` (A_(1))/(A_(2)) = (2)/(1)`

Discussion

47.	For one series A.C. circuit, its reactance is equal to its resistance. Then its power factor is ……….
Answer» 1 `1/2` `1/sqrt2` 0 Solution :If `phi` is the PHASE difference between voltage and current in series A.C. circuit then we have : tan `phi=(X_L-X_C)/R=1`(`because` Here `X_L-X_C=R`) `therefore phi=45^@=pi/4` rad Now , POWER FACTOR `=cos phi =cos 45^@ =1/sqrt2`

Discussion

48.	A network of resistore is connected to a 16 V battery with internal resistance of 1Omega, as shown in (a) Compute the equivalent resistance of the network. (b) Obtain the current in each resistor.(c ) obtain the voltage drops V _(AB), V _(BC) and V _(CD)
Answer» 7 OHMS, 4V, 2V and 8V 2 ohms, 4V, 2V and 8V 7 ohms, 4V, 4V and 8V 6 ohms, 4V, 2V and 4V Answer :A

Discussion

49.	The fig. represents the observed intensity of X-rays emitted by an X-ray tube as a function of wavelength. The sharp peaks A and B denote
Answer» CONTINUOUS SPECTRUM BAND spectrum characteristic spectrum white radiations Answer :C

Discussion

50.	Radio waves of constant amplitude can be generated with :
Answer» Filter Rectifier F.E.T. Oscillator. Answer :D

Discussion

Explore topic-wise InterviewSolutions in Current Affairs.

Two resistors with temperature coefficients of resistane alpha_(1) and alpha_(2) have resistances R_(1) and R_(2) at0^(@)C. Find the temperature coefficient of the compound resistor consisting of the two resistors connected in parallel

Find the number density of impurity atoms that must be added to a pure silicon crystal inorder to convert it to have resistivity (i) 10^(-1) Omegam n-type silicon (ii) 10^(-1)Omegam p-type silicon. Give for silicon: mu_(e)=0.135m^(2)V^(-1)s^(-1) and mu_(h)=0.048m^(2)V^(-1)s^(-1).

Two identical flutes produces fundamental nodes of frequency 300 Hz at 27°C. If the temperature of air in one flute is increases to 31°C the number of the beats per second will be (approx)

The path difference for destructive interference is.....

Statement-I : Soft and hard X–rays differ in frequency. Statement-II : Hard X-rays propagate at higher speed than soft X-rays.

Photoelectric current still continues when the anode is even at a slight negative potential with respect to the photo cathode. Explain.

In a negative feedback amplifier, the gain without feedback is 100, feed back ratio is 1/25 and input voltage is 50 mV. Calculate feedback voltage

In a negative feedback amplifier, the gain without feedback is 100, feed back ratio is 1/25 and input voltage is 50 mV. Calculate feedback factor

In a negative feedback amplifier, the gain without feedback is 100, feed back ratio is 1/25 and input voltage is 50 mV. Calculate output voltage

In a negative feedback amplifier, the gain without feedback is 100, feed back ratio is 1/25 and input voltage is 50 mV. Calculate gain with feedback

What is the moment of inertia of a thin rod of length L and mass M about an axis passing through one end and perpendicular to its length?

The audio signal cannot be transmitted directly to space. Why?

What was Think Tank's view about the earthlings at last?

In the cirucit (figure6.3) resistance R_(1) and R_(2) are known and cells ar of emf e_(1) and e_(2) and negligible internal resistance. At what valueof R will the thermal power generated in it be the highest? What is it equal to?

A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10^(-12)F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6?

A long copper tube of inner radius R carries a current I. The magnetie field B inside the tube is

In a transistor configuration, p parameter is:

Which of the following atoms has permanent electric dipole moment zero ?

Ozone layer blocks the radiation of wavelength

(A):Displacement of a body may be zero when distance travelled by it Is not zero. (R ):The displacement is the longest distance between initial and final positions.

At t=0, an inductor of zero resistance is joined to a cell of emfepsi through a resistance. The current increases with a time constant tau . After what time will the potential difference across the coil be equal to that across the resistance ?

A ray of light is incident on a rectangular plate at an angle of incidence 60^(@). The light ray suffers a deviation which is 25% of the angle of incidence. The refractive index of the glass will be

A positively charged ring is in y - z plane with its centre at origin . A positive test charge q_(e ) , held at origin is released along x axis, then its speed

What is an alpha-particle ? state it's characteristics ?

A hollow equilateral air prism is immersed in water. Calculate the deviation of a ray incident at an angle 30^(@) from the base side (.^(a)mu_(w)=(4)/(3))

If momentum /(p), area a and time (t) are taken to be the fundamental quantities then the energy has the dimensional formula:

The de Broglie wavelength of an electron is 1A^(@). In what potential difference electron accelerates

A liquid risestoa height of 9 cm in a glass liquid column in a glass capillary of radius 0.03 cm is

As soon as current is switched on in a high voltage wire, the bird sitting on it flies away why ?

State the types of degrees of freedom of non-rigid diatomic molecules.

Two rods of equal length and diameter but of thermal conductivities 1.5 and 3 S.I. units respectivity of combination is :

If a load of 6 k Omega is used, then the voltage gain of the amplifier is ……… .

What we call the ratio of angle of deviation to change in wavelength ?

The ratio of the deBroglie wavelengths of proton, deuteron and alpha particle accelerated through the same potential difference 100V is

A series LR circuit is connected to an ac source of frequency omega and the inductive reactance is equal to 2R. A capacitance of capacitive reactance equal to R is added in series with L and R. The ratio of the new power factor to the old one is

Two wires of the same material and having the same length but their diameters are in the ratio of 3/2. The ratio of strain energy per unit volume when they are streched will be

Refractive index of lonosphere is

A microscope consists of two convex lenses of focal lengths 2.0 cm and 6.25 cm placed 15.0 cm apart. Where must the object be placed so that the final virtual image is at a distance of 25 cm from the eye?

The ratio of energy of the hydrogen atom in its first and second excited state is:

In the Young's double -slit experiment, the interference pattern is found to have intensity ratio between bright and dark fringes as 9.This implies that

For one series A.C. circuit, its reactance is equal to its resistance. Then its power factor is ……….

A network of resistore is connected to a 16 V battery with internal resistance of 1Omega, as shown in (a) Compute the equivalent resistance of the network. (b) Obtain the current in each resistor.(c ) obtain the voltage drops V _(AB), V _(BC) and V _(CD)

The fig. represents the observed intensity of X-rays emitted by an X-ray tube as a function of wavelength. The sharp peaks A and B denote

Radio waves of constant amplitude can be generated with :