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Electromagnetism and Materials MCQs

Total questions: 91

Worksheet time: 46mins

Name
Class
Date
1.

The interaction energy between two distant electric dipoles r goes like

a)

r−1r^{-1}

b)

r−2r^{-2}

c)

r2r^{2}

d)

r−3r^{-3}

2.

If the magnetization vector M in a material is equal to M(x,y,z) = axi + byj + czk, where a, b and c are constants of suitable size, the amperian currents inside the material

a)

depend from the values of a, b and c

b)

The question is wrong: the amperian currents don't depend on M

c)

are zero

d)

are different from zero

3.

In an anisotropic dielectric material

a)

the polarization P is parallel to the electric field E but not to the dielectric induction vector D

b)

the polarization P is not parallel neither to the electric field E nor to the dielectric induction vector D

c)

the polarization P is always parallel to both the electric field E and to the dielectric induction vector D

d)

the polarization P is parallel to the dielectric induction vector D but not to the electric field E

4.

Under what conditions is the vector magnetic solenoidal and conservative?

a)

Only in steady state.

b)

When rot B = 0

c)

When there are no charges.

d)

Always.

5.

An electromagnetic wave having a frequency of 1.8×1012Hz1.8 \times 10^{12} Hz propagates at the speed v=2.7×108m/sv = 2.7 \times 10^{8} m/s . Determine the value of the wavelength λ\lambda and of the period TT .

a)

λ = λλ = 1.5 × 10^{-3} m, T = TT = 5.55 × 10^{-13} s

b)

λ = λλ = 1.5 × 10^{-4} m, T = TT = 5.55 × 10^{-12} s

c)

λ = λλ = 1.5 × 10^{-4} m, T = TT = 5.55 × 10^{-13} s

d)

λ = λλ = 1.5 × 10^-4 m, T = TT = 5.55 × 10^-35 s

6.

The magnetic field generated at a point P by a moving (non-relativistic) charge

a)

is inversely proportional to the distance between the charge and the point P

b)

does not depend on the direction of motion of the charge

c)

is inversely proportional to the square of the distance between the charge and the point P

d)

does not depend on the distance between the charge and the point P

7.

If the intensity of a plane electromagnetic wave is i1 at the point x1 along the direction of propagation, at the point x2 = 2x1 the intensity i2 will be

a)

i2 = i1/2

b)

i2 = 2i1

c)

i2 = i1/4

d)

i2 = i1

8.

The ratio of the tangential components B1t and B2t of the magnetic field B measured at the interface between two materials having χ1m = 0.3 and χ2m = 0.5 respectively, magnetic susceptibility is

a)

B1t/B2t = 0.87

b)

B1t/B2t = 1.67

c)

B1t/B2t = 1.15

d)

B1t/B2t = 0.60

9.

In a region of empty space there exists a vector A(x,y,z) = a x i + b y j + c t k and an electrical potential V(x,y,z) = − d y, (where a, b, c and d are suitably sized constants). What is the electric field E?

a)

E = − (a t + d)i − bj - c k

b)

E = d j − c k

c)

E = − a i + d j

d)

E = (a − d) x i

10.

When an electromagnetic wave passes from one medium to another, what happens to the frequency and V the wavelength λ?

a)

λ changes, V remains the same

b)

λ remains the same, V remains the same

c)

λ remains the same, V changes

d)

λ changes, V changes

11.

To an electric field E = a t k, where a is a constant of suitable size, is associate a displacement density of current js

a)

js = ε0 a k

b)

js = μ0 ε0 a k

c)

js = a k

d)

js = μ0 ε0 ak

12.

If the polarization vector P(x,y,z) = a x i + b y j + 5 c k is present in a dielectric material, where a, b and c are constants of suitable size, when just surface polarization charges are present?

a)

when a = b

b)

when a = − b − 5 c

c)

always

d)

when a = − b

13.

Kirchhoff’s second law is another way of expressing

a)

the energy conservation

b)

the fact that the magnetic field is solenoidal

c)

the conservation of momentum

d)

the conservation of charge

14.

What is the power P dissipated in a superconductor wire crossed by a current I?

a)

P = V

b)

P=R2I2P=R^2I^2

c)

P=RI2P=RI^2 as in a normal metal

d)

P = 0

15.

In a region of space there is an electric field E(x,y,z,t) = 2 a t i − 4 b y j + 3 b z k, where a and b are constants of suitable size. What is the value of the charge density ρ present in this region of space?

a)

ρ = (2 a t + b) ε0

b)

ρ = b ε0

c)

ρ = 0

d)

ρ = -b ε0

16.

A rectilinear infinite wire, immersed in a material having magnetic permeability km = 1.2, is crossed by a current I = 5 A. Calculate the modulus of the magnetic field B generated by the wire at a distance r = 0.2 m.

a)

B = 6.0×10−6 T6.0 \times 10^{-6}\,\text{T}

b)

B = 12.0×10−6T12.0\times10^{-6}\text{T}

c)

B = 2.4×10−7 T2.4 \times 10^{-7}\,\text{T}

d)

B = 2.4×10−4 T2.4 \times 10^{-4}\,\text{T}

17.

In an anisotropic dielectric material the vector is P(x,y,z) = 2 a z i − 3 b y j + c x k, where a, b and c are constants of suitable size. Determine the value of the volume polarization charge density ρρ present in the dielectric material.

a)

ρρ = (2 a − 3 b) ε0

b)

ρρ= − 3 b ε0

c)

ρρ = 3 b

d)

ρρ = 3 b ε0

18.

In an energy part of space there is a uniform electric field E linearly increasing in time. The circuitry of field B along a closed line, contained within this part of space, is

a)

constant

b)

zero

c)

decreasing linearly over time

d)

growing linearly over time

19.

The magnetic susceptibility of a paramagnetic material

a)

has a dependence of the type T−1T^{-1} on temperature

b)

does not depend on temperature

c)

grows linearly with temperature

d)

decreases linearly with temperature

20.

In an anisotropic material the magnetization vector M is M = a x i + b y j + c z k, where a, b and c are suitably sized constants. Determine the density of magnetization current jm present within the material.

a)

jm = a (y − z) i + b (z − x) j + c (x − y) k

b)

jm = − a i − b j − c k

c)

jm = a i + b j − c k

d)

jm = 0

21.

In an empty part of space there is a uniform electric field EEE increasing over time such as t2t^2t2 . The circuitry of the magnetic field B along a closed line totally contained within this part of space is

a)

constant

b)

increasing linearly over time

c)

decreasing linearly over time

d)

zero

22.

The ratio of the normal electric field components E1nE_{1n} and E2nE_{2n} measured at the interface between two homogeneous and isotropic dielectrics, having electric susceptibility equal to χ1=0.5\chi_1 = 0.5 and χ2=0.8\chi_2 = 0.8 respectively, is

a)

E1n/E2n=1.000E_{1n}/E_{2n} = 1.000

b)

E1n/E2n=0.833E_{1n}/E_{2n} = 0.833

c)

E1n/E2n=1.200E_{1n}/E_{2n} = 1.200

d)

E1n/E2n=1.600E_{1n}/E_{2n} = 1.600

23.

The resistivity of a metal at a temperature close to room temperature

a)

is an increasing linear function of temperature

b)

is a linear decreasing function of temperature

c)

depends on the geometric characteristics of the object on which the measurement is made but it doesn’t depend on temperature

d)

is independent of the geometric characteristics of the object on which it is measured

24.

Calculate the drift velocity Vd of the conduction electrons inside a metal wire of cross‑section S = 3 mm2 crossed by a current I = 5 A. Assume that the density of the carriers n is equal to 3×1028 m−33 \times 10^{28}\,\text{m}^{-3} .

a)

Vd = 3.47×10−5 m/s3.47 \times 10^{-5}\,\text{m/s}

b)

Vd = 1.74×10−3 m/s1.74 \times 10^{-3}\,\text{m/s}

c)

Vd = 3.47×10−4 m/s3.47 \times 10^{-4}\,\text{m/s}

d)

Vd = 1.74×10−4 m/s1.74 \times 10^{-4}\,\text{m/s}

25.

The electrostatic field is conservative

therefore

a)

its circulation along any closed path is zero

b)

it has zero gradient

c)

it has zero divergence

d)

its flow through any closed surface is zero

26.

Iron at temperatures above the critical behaves

a)

in a way that depends on the particular type of magnetic field that has been applied to the material

b)

like a paramagnet

c)

like a diamagnet

d)

like a ferromagnet

27.

Kirchhoff’s first law is another way of expressing

a)

the conservation of charge

b)

the energy conservation

c)

the conservation of momentum

d)

the fact that the magnetic field is solenoidal

28.

The phenomenon diffraction occurs only in the presence of flat electromagnetic waves.

a)

False

b)

True but it occurs if the waves are also harmonic electromagnetic waves

c)

True but it occurs only if the waves are also harmonic electromagnetic waves and not in the vacuum

d)

True

29.

The vector E(x,y,z) = a y i + a x j + b z k, with a and b constants of appropriate size, can represent an electrostatic field?

a)

Yes, but just when a ≠ b

b)

Yes, because div E = 0

c)

Yes, because rot E = 0

d)

Yes, because div E ≠ 0

30.

In an anisotropic dielectric material

a)

the polarization P is parallel to the dielectric induction vector D but not to the electric field E

b)

the polarization P is always parallel to the electric field E and to the dielectric induction vector D

c)

the polarization P is parallel to the electric field E but not to the dielectric induction vector D

d)

the polarization P is not parallel neither to the electric field E nor to the dielectric induction vector D

31.

Gauss' law states that

a)

the flow of total electric field, generated by all the charges through a closed surface, is equal to the algebraic sum of charges contained there divided by the dielectric constant of vacuum

b)

the flow of the electric field through a closed surface is always zero

c)

the flow of the electric field through any surface is equal to the algebraic sum of the charges contained in it divided by the dielectric constant of vacuum

d)

the flow of the electric field through a surface is equal to the sum of the modules of the charges contained in it divided by the dielectric constant of vacuum

32.

A rigid square coil of side a = 20 cm is crossed by a current I = 2 A and is placed in a magnetic field of modulus B = 0.03 T whose direction forms an angle θ = 30° with the normal on the plane on which the coil lies. Determine the modulus of torque M acting on the loop

a)

1.2 × 10-2 Nm

b)

2.4×10−4Nm2.4 \times 10^{-4} Nm

c)

1.2 × 10-3 Nm

d)

M = 0 Nm

33.

Solving Maxwell's equations of electromagnetism means

a)

to calculate the charge distributions Q and current distribution i, knowing the fields E and B

b)

to satisfy the continuity equation ∇×j + ∂ρ/∂t = 0

c)

to calculate the distribution of charge densities ρ and current densities j, knowing the fields E and B

d)

to calculate the fields E and B, knowing the distributions ρ of the charge densities, j of the current densities and the boundary conditions

34.

A monochromatic light beam (λ = 644 nm) passes through a rectangular slit a rid forms a figure of diffraction in which the first dark fringe corresponds Θ = 0.125°. What is the width of the slit?

a)

2.95 × 10-4 m

b)

1.66 × 10-4 m

c)

3.8 × 10-4 m

d)

1.25 × 10-4 m

35.

In a dielectric material the sum of the surface polarization charges is zero when

a)

the material is homogeneous

b)

never

c)

the applied electric field has a particular value

d)

always

36.

The bulk density of amperian currents jm, in a material with magnetization vector M, is equal to

a)

jm = div M

b)

jm = rot M

c)

jm = M × n

d)

jm = grad M

37.

Two straight parallel wires of indefinite length, placed in the empty space and distant from each other, are crossed by two concordant currents I1 and I2. Determine the strength B of the magnetic field in the point placed in the middle of the right line joining the two wires

a)

B = μ0 | I1 + I2 | /πd

b)

B = μ0 | I1 + I2 | /2πd

c)

B = μ0 | I1 - I2 | /2πd

d)

B = μ0 | I1 − I2 | /πd

38.

A particle with mass and charge, initially at rest, is immersed in a magnetostatic field B and electrostatic field E, vectorially parallel to each other and uniformly distributed in space. The motion assumed by the charge is

a)

helical

b)

uniform circular

c)

uniformly accelerated straight line

d)

uniform straight line

39.

The energy dissipated by the Joule effect during the exchange of the capacitor in an RC circuit is equivalent to

a)

RC

b)

R/C

c)

by generator to charge the capacitor

d)

the electrostatic energy of the capacitor

40.

The mutual induction coefficient M between two circuits does NOT depend on

a)

the distance between the two circuits

b)

the intensity of current moving in the two circuits

c)

the medium which is interposed between the two circuits

d)

the shape of the two circuits

41.

What is the value of rotor of electrostatic field E(x,y) = yi(x2+y2)−xj(x2+y2) ?

a)

rotE = 0. E is conservative everywhere

b)

rotE ≠ 0. E is non-conservative

c)

rotE = 0. E is conservative in R2 = [0,0]

d)

rotE = 0. E is non-conservative in R₂ = [0,0]

42.

Gauss's law for the magnetic necessarily provides

a)

the flow of B is always zero if there are no currents

b)

the flow of B across a surface is always zero

c)

the flux of B is always zero if the magnetization of the material is negligible

d)

there are no magnetic monopoles

43.

The Hall effect can be used

a)

to measure a magnetic field

b)

to determine the intensity of an electromagnetic wave

c)

to determine the dielectric strength of an insulator

d)

to determine the mobility of the ions in a generic metal

44.

Gauss's law for the electric field E necessarily provides

a)

the charges are point-like

b)

the surface on which to calculate the flow of E is spherical

c)

the surface on which to calculate the flow of E is closed

d)

field E does not depend on time

45.

The electrostatic field is conservative therefore it

a)

its circulation along some closed path is zero

b)

has zero curl

c)

has zero gradient

d)

its flow through any closed surface is zero

46.

Which of the following properties of the induction vector D is correct?

a)

D = E − P

b)

D = εr E for each type of dielectric material

c)

∫\int ∫\int D ⋅ n dΣ = Q where Q is the free charge inside the unit vector n

d)

∫\int ∫\int D ⋅ n dΣ = 0 where Σ is a closed surface with normal unit vector n

47.

In a paramagnet magnetic susceptibility

a)

depends on the applied magnetic field

b)

does not vary with temperature

c)

grows with temperature

d)

decreases with temperature

48.

An electron of charge e and velocity of module v completes a semicircle of radius R due to a magnetic field of module B placed perpendicular to v. How much is the work W done by Lorentz force worth?

a)

W = π e v B R J

b)

W = 2 π e v B R J

c)

W = π e v B R / 2 J

d)

W = 0 J

49.

The energy associated in a given volume with the presence of an electric field is larger when

a)

it doesn't depend on what's in the volume

b)

the volume is filled with a dielectric material

c)

the volume is filled with a non-homogeneous dielectric material

d)

the volume is empty

50.

The field B(x,y,z) = a x i + 2 b y j + 4 c z k (where a, b and c are constants of suitable size) exists in nature?

a)

Always

b)

Just when b = 0

c)

Just when a = 0

d)

Just when a = −2 b − 4 c

51.

In an anisotropic material the magnetization vector is M=ay i^+bx j^+cz k^\mathbf{M}=a y\,\hat{\mathbf{i}}+b x\,\hat{\mathbf{j}}+c z\,\hat{\mathbf{k}} (where aa , bb , and cc are constants of suitable size). When is the density of magnetization current jm\mathbf{j}_m present within the material is zero?

a)

a=ba=b

b)

a=b+ca=b+c

c)

a=−b−ca=-b-c

d)

a=−ba=-b

52.

A dielectric material, homogeneous and isotropic, is immersed in a uniform external electrostatic field. The sum of the polarization charges on the surface of this material is

a)

always different from zero

b)

non-zero only if the object has a regular shape

c)

zero only if the object has a regular shape

d)

always zero

53.

The intensity of a cylindrical wave at a distance rr from the source

a)

decreases as 1/r1/\sqrt{r}

b)

decreases as 1/r21/r^2

c)

doesn't change

d)

decreases as 1/r1/r

54.

An electric field generated by a distribution of charges is electrostatic if and only if

a)

the distribution of charges is spherical or point-like

b)

the test charge is at rest

c)

the test charge is in uniform rectilinear motion

d)

the distribution of charges is at rest

55.

Which of the following parameters that characterize a harmonic wave does not change when it passes between two materials with different refractive index?

a)

speed

b)

wavelength

c)

wave number

d)

frequency

56.

At electrostatic equilibrium, the E\mathbf{E} field near the surface of a charged conductor with a uniform negative surface charge density σ\sigma is

a)

uniform, parallel to the surface, of the direction entering the conductor

b)

uniform, perpendicular to the surface, of the direction entering the conductor

c)

uniform, perpendicular to the surface, facing out from the conductor

d)

anywhere null

57.

The charge qq on the surface armatures SS of an empty plane capacitor varies as a function of time with the law q(t)=at+bq(t)=a t + b (where aa and bb are constants of suitable size). Calculate the displacement current density JdJ_d that flows across the capacitor.

a)

Jd=4at3SJ_d=\frac{4at^3}{S}

b)

Jd=aSJ_d=\dfrac{a}{S}

c)

Jd=ε0aSJ_d=\dfrac{\varepsilon_0 a}{S}

d)

Jd=ε0atSJ_d=\dfrac{\varepsilon_0 a t}{S}

58.

If rr is the distance from the source, the intensity of a spherical wave

a)

varies as 1/r21/r^2

b)

increases proportionally to rr

c)

does not depend on rr

d)

decreases proportionally to 1/r1/r

59.

The magnetic field B(x,y,z)=ax i^−by j^+5cx k^\mathbf{B}(x,y,z)=a x\,\hat{\mathbf{i}}-b y\,\hat{\mathbf{j}}+5 c x\,\hat{\mathbf{k}} (where aa , bb and cc are constants of a suitable size) is conservative

a)

just when b=0b=0

b)

just when c=0c=0

c)

just when a=0a=0

d)

always

60.

If M=χm(T) H\mathbf{M}=\chi_m(T)\,\mathbf{H} this material is

a)

diamagnetic and paramagnetic

b)

paramagnetic

c)

ferromagnetic because χm(T)\chi_m(T) doesn’t depend on H\mathbf{H}

d)

diamagnetic

61.

At a point of coordinates (x;y;z)(x;y;z) in a conducting medium, the current density has the expression j(x,y,z)=3x2yux−3xy2uy+xyuzj\left(x,y,z\right)=3x^2yu_x-3xy^2u_y+xyu_z . What can be said about the charge density ρ\rho at that point?

a)

nothing can be said about ρ\rho

b)

ρ\rho is constant

c)

ρ\rho decreases over time

d)

ρ\rho increases over time

62.

We want to make a circuit RL using an inductance LL and two resistors R1R_1 and R2R_2 . The resistors can be connected together in series or in parallel. Which of the following statements is right?

a)

the rapidity of the transients RL does not depend on the connection

b)

the transients of the RL circuit are faster if R2>R1R_2>R_1

c)

the transients of the RL circuit are faster if two transistors are connected in parallel

d)

the transients of the RL circuit are faster if two transistors are connected in series

63.

The gap between the plates of a capacitor, initially empty, is completely filled with a dielectric material. With the same charge on the plates

a)

the capacitance decreases, the electrostatic field increases

b)

the capacitance increases, the electrostatic field decreases

c)

the capacitance and the electrostatic field increase

d)

the capacitance and the electrostatic field decrease

64.

Iron at temperatures below the critical temperature behaves

a)

like a ferromagnet

b)

like a paramagnet

c)

in a way that depends on the particular type of magnetic field that has been applied to the material

d)

like a diamagnet

65.

In an isotropic material B=μ H\mathbf{B}=\mu\,\mathbf{H} . This means that H\mathbf{H} is always solenoidal.

a)

yes but just in a diamagnetic material

b)

yes

c)

yes but just in the paramagnetic and ferromagnetic materials

d)

no

66.

A parallel plane plate is entirely filled with a homogeneous and isotropic dielectric material with relative dielectric constant κr=3\kappa_r=3 placed perpendicularly to an external electric field of modulus E0=15 V/mE_0=15\ \mathrm{V/m} . How much is worth the polarization module PP ?

a)

P=2.65×10−10 C/m2P=2.65\times10^{-10}\ \mathrm{C/m^2}

b)

P=8.85×10−11 C/m2P=8.85\times10^{-11}\ \mathrm{C/m^2}

c)

P=8.85×10−12 C/m2P=8.85\times10^{-12}\ \mathrm{C/m^2}

d)

P=3.98×10−9 C/m2P=3.98\times10^{-9}\ \mathrm{C/m^2}

67.

Under what conditions is the vector magnetic field B\mathbf{B} solenoidal?

a)

in the vacuum

b)

always

c)

when there are no charges

d)

only in steady state

68.

In a region of empty space there exists potential vector A(x,y,z,t)=atxi + byj+czkA\left(x,y,z,t\right)=atxi\ +\ byj+czk (where aa , bb and cc are constants of suitable size). How much is the associated magnetic field B\mathbf{B} ?

a)

B=ci−atj+bkB=ci-atj+bk

b)

B=ai+bj+ckB=ai+bj+ck

c)

B=ati+bj+ckB=ati+bj+ck

d)

B=0\mathbf{B}=0

69.

The electrical potential inside a metallic material is

a)

null only if the metallic object has a spherical shape

b)

constant

c)

dependent on the shape of the metallic object

d)

null

70.

A resistance of 8 Ω8\ \Omega must be made but only 3 valuable resistors are possessed: R1=5 ΩR_1=5\ \Omega , R2=4 ΩR_2=4\ \Omega and R3=12 ΩR_3=12\ \Omega . How can the necessary resistance be achieved?

a)

by connecting the three resistors in parallel

b)

by connecting the three resistors in series

c)

by connecting R2R_2 and R3R_3 in parallel and R1R_1 in series with the previous parallel

d)

by connecting R1R_1 and R2R_2 in series and R3R_3 in parallel to the series

71.

The polarization vector P\mathbf{P} generated in an isotropic and homogeneous material with relative dielectric constant εr\varepsilon_r immersed in an external electrostatic field E0E_0

a)

is equal to ε0(εr−1)E0\varepsilon_0(\varepsilon_r-1)E_0

b)

is equal to (εr−1)E0(\varepsilon_r-1)E_0

c)

is equal to ε0(εr−1)E0/εr\varepsilon_0(\varepsilon_r-1)E_0/\varepsilon_r

d)

is equal to (εr−1)E0/εr(\varepsilon_r-1)E_0/\varepsilon_r

72.

Inside a homogeneous dielectric material without free charges

a)

there may be volume polarization charges but only for particular materials

b)

there can be no volume polarization charges

c)

there can be no surface polarization charges

d)

there may be volume polarization charges

73.

The electrical conductivity σ in the Drude model

a)

depends on the electric field

b)

depends on the square of the density of carriers

c)

doesn't depend on the sign of carriers

d)

doesn't depend on the mean time interval between two successive collision

74.

Considering the phenomenon of electrical polarization in a generic dielectric material, which of the following is correct

a)

The modulus of the electric induction vector D represents a polarization charge per unit area.

b)

The polarization P is always parallel to the electric field vector E within the material.

c)

The polarization P is never parallel to the electric field vector E within the material.

d)

Above the threshold value of the electric field E, the modulus of the polarization vector P tends asymptotically to a maximum saturation value.

75.

Curie's law for a ferromagnet states that magnetic susceptibility is

a)

Xm = Cρ(T − Tc)

b)

Xm = Cρ/(T − Tc) for T > Tc

c)

Xm = Cρ/(T − Tc) for T < Tc

d)

Xm = Cρ/T

76.

For an electric charge to move with constant speed in a region in which there is an electric field

a)

the motion must take place on an equipotential surface

b)

the motion must take place along a line of force of the field

c)

the electric field must be conservative

d)

the electric field must be uniform

77.

The density of electric current j at each point within a conductor

a)

is parallel to electric field E in the conductor only if the carriers are positive

b)

is always zero

c)

is always parallel to electric field E

d)

is parallel to the electric field E in the conductor only if the carriers are negative

78.

An electromagnetic wave carries quantities of motion. Consequently when it affects a surface it applies a force to it. Which of the following statements is true?

a)

the force applied is maximum if the surface is totally absorbent

b)

the applied force is the same whether the surface is totally reflective or totally absorbent

c)

the force applied is maximum if the surface is totally reflective

d)

the applied force is minimal if the surface is totally reflective

79.

The magnetic susceptibility of a diamagnetic material

a)

has a dependence of the type T-1 on temperature

b)

does not depend on the temperature

c)

grows linearly with temperature

d)

decreases linearly with temperature

80.

In order to observe the phenomenon of interference between the waves emitted by two coherent sources, it is necessary that

a)

the difference of path that the two waves must travel to reach a on the screen must be much less than their length

b)

the two waves propagate in different media

c)

the two waves propagate in the same medium

d)

the difference of path that the waves must travel to reach a on the screen must be much greater than their length

81.

In the classic model of electrical conduction (Drude model)

a)

the intensity of electric current j is independent of the applied electric field E

b)

the drift speed of the carriers is independent of the applied electric field E

c)

the electric current density j is independent of the applied electric field E

d)

the electrical conductivity is independent of the applied electric field E

82.

In a Young experiment, the maximum of order one is subtended at an angle θ = 30°. It can be deduced that

a)

the distance the sources is half the wavelength

b)

the distance between the sources is double the wavelength

c)

the distance between the sources and the screen is double the wavelength

d)

the distance between the sources and the screen is half the wavelength

83.

The second law of Laplace provides that the force applied on a closed circuit crossed by a stationary current I on which a uniform magnetic field B acts is

a)

non-zero if field B is parallel to the circuit

b)

different from zero if field B is orthogonal to the circuit

c)

only on the area enclosed by the circuit

d)

always zero

84.

The law of reflection of geometric optics

a)

depends on on the characteristics of the material in which the light beam propagates

b)

does not depend on on the characteristics of the material in which the light beam propagates

c)

depends on the frequency of the light beam

d)

depends on the width of the light beam

85.

An indefinite cylinder is traversed by a current parallel to the axis of the cylinder itself with uniform and stationary current density j. The field B inside the cylinder

a)

grows linearly as the distance r from center increases

b)

is not known. The data of problem are not sufficient to answer

c)

is always null

d)

does not vary with the distance r from the cylinder axis

86.

Given a sphere with a uniform charge density ρ, E is the field inside the sphere?

a)

E is always constant

b)

E is equivalent to that generated by a point charge placed in the center

c)

E grows linearly as the distance r from the center increases

d)

E is always null

87.

A spherical shaped body is made of insulating material and with uniform charge density. The body has a spherical cavity inside, not concentric with respect to it. By indicating with Φz(E) the flow of the electrostatic field through a closed surface Z completely contained in the cavity, and with E(C) the electrostatic field at the center C of the cavity, which of the following statements is true?

a)

ΦΣ(E) = 0, E(C) = 0

b)

ΦΣ(E) ≠ 0, E(C) ≠ 0

c)

ΦΣ(E) = 0, E(C) ≠ 0

d)

ΦΣ(E) ≠ 0, E(C) = 0

88.

A wavelength radiation in the vacuum λ = 600 nm propagates in a transparent dielectric medium. with a refractive index If the wavelength in the medium is reduced to λ = 400 nm, the relative constant of medium εr is

a)

εr = 1.50

b)

εr = 1.23

c)

εr = 0.44

d)

εr = 2.25

89.

The amplitude of the magnetic field of a plane harmonic wave that propagates in vacuum is worth
B0 2 × 10-6 T. What is the maximum value of its Poynting vector S?

a)

Smax = 478W/m2478W/m^2

b)

Smax = 2.66×10−9W/m22.66 \times 10^{-9} W/m^{2}

c)

Smax = 5.31×10−9W/m25.31 \times 10^{-9} W/m^2

d)

Smax = 956W/m2956 W/m^2

90.

The vacuum capacitance of a spherical capacitor whose external armature has twice the radius of the internal one (R2 = 2R1) is

a)

C = 4πε00R1

b)

C = 8πε00R1

c)

C = 8πε00R2

d)

C = 4πε0R124\piε_0R_1^2

91.

In a ferromagnet the shape of hysteresis cycle depends

a)

from the particular ferromagnetic material and from the applied field H

b)

just from the particular ferromagnetic material

c)

it is equal for all ferromagnetic materials

d)

from the applied field H

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