Mix Test

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Mix Test - 9

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Weekly Quiz Competition

Question 1
1 / -0

Which among the following, is not a cause for power loss in a transformer-

A
Eddy currents are produced in the soft iron core of a transformer.

B
Electric Flux sharing is not properly done in primary and secondary coils.

C
Humming sound produed in the tranformers due to magnetostriction.

D
Primary coil is made up of a very thick copper wire.

Solution

Primary coil made of Thick Coper wire has very less R. Therefore negligible power loss. Rest all options are reasons for power losses in a transformer.
Question 2
1 / -0

A battery is connected to the conductor of non-uniform cross section area. The quantities or quantity which remains constant is-

A
Electric field only

B
Drift speed and electric field

C
Electric field and current

D
Current only

Solution

Rest all quantities change with area of cross-section of a conductor.
Question 3
1 / -0

The current sensitivity of a galvanometer increases by 20%. If its resistance also increases by 25%, the voltage sensitivity will.

A
Decrease by 1%

B
Increased by 5%

C
Increased by 5%

D
Decrease by 4%

Solution

Given, \(I'g=I_g+\frac{20}{100}I_g\)

\(=\frac{120}{100}I_g=1.2I_g\)

\(R'=R+\frac{25}{100}R=\frac{125}{100}R\)

= 1.25 R

V'g = ?

V'g = \(\frac{I_g}{R'}=\frac{1.2I_g}{1.25 R}\)

= \(\frac{120}{125}V_g=\frac{25}{25} V_g\)

% change = \(\frac{V'g-V_g}{V_g}\times100\)

\(=\frac{\left(\frac{24}{25}V_g-V_g\right)}{V_g}\times100\)

\(=\frac{(24-25)}{25}\times100\)

\(=\frac{-1}{25}\times100\) = 4%

Decrease by 4%
Question 4
1 / -0

In a hydrogen atom the electron moves in an orbit of radius 0.5 Å making 10 revolutions per second, the magnetic moment associated with the orbital motion of the electron will be

A
\(2.512 \times 10^{-38} Am^2\)

B
\(1.256 \times 10^{-38} Am^2\)

C
\(0.628 \times 10^{-38} Am^2\)

D
Zero

Solution

R = 0.5 \(A^{\circ}\)

\(\omega \) = 10 rps = 10 \(\times2\pi\) rad/s

v = 10 Hz

M = I A = e v \(\pi\,r^2\)

\(=1.6\times10^{-19}\times10\times3.14\times0.5\times0.5\)\(\times10^{-10}\times10^{-10}\)

\(=1.256\times10^{-38}\) A\(m^2\)
Question 5
1 / -0

An air-cored solenoid with length 30 cm, area of cross-section 25 \(cm^2\) and number of turns 800, carries a current of 2.5 A. The current is suddenly switched off in a brief time of \(10^{-3}\) s. Ignoring the variation in magnetic field near the ends of the solenoid, the average back emf induced across the ends of the open switch in the circuit would be

A
zero

B
3.125 volts

C
6.54 volts

D
16.74 volts

Solution

Magnetic field inside a solenoid

\(B=\mu_0\frac{N}lI'\)

Flux linked with ‘N’ turns

Initial flux \(\phi_1=\) N B A = N\(\mu_0\frac{N}{l}\) I A

\(=\mu_0\frac{N^2}lIA\)

\(=\frac{4\pi\times10^{-7}\times800\times800\times2.5\times2.5\times10^{-4}}{0.30}\)

= 16.74 \(\times10^{-3}\) Wb

Final flux \(\phi_2=0\)

Average back emf |e| = \(\frac{d\phi}{dt}=\frac{16.74\times10^{-3}-0}{10^{-3}}\)

= 16.74 V
Question 6
1 / -0

A sinusoidal voltage of peak value 283 V and frequency 50 Hz is applied to a series LCR circuit in which R = 3 \(\Omega\), L = 25.48 mH, and C = 796 \(\mu\)F, then the power dissipated at the resonant condition will be-

A
39.70 kW

B
26.70 kW

C
13.35 kW

D
Zero

Solution

\(V_o\)= 283 V, f = 50 Hz

R = 3 \(\Omega\), L = 25.48 mH

C = 796 \(\mu\)F

P |at resonance = ?

Power dissipated P = \(I^2\)R

\(I=\frac{I_0}{\sqrt2}=\frac{1}{\sqrt2}\left(\frac{283}{3}\right)\)

= 66.7 A

P = \(I^2\)R

= \((66.7)^23\)

= 13.35 kW
Question 7
1 / -0

If both the number of turns and core length of an inductor is doubled keeping other factors constant, then its self-inductance will be-

A
Unaffected

B
Doubled

C
Halved

D
Quadrupled

Solution

L = \(\mu_0\frac{N^2}{l}A\)

L' = \(\mu_0\frac{(2N)^2}{2l}A\)

\(=2\mu_0\frac{N^2}lA\) = 2L
Question 8
1 / -0

Assertion (A): To increase the range of an ammeter, we must connect a suitable high resistance in series to it.

Reason (R): The ammeter with increased range should have high resistance.

A
Both A and R are true and R is the correct explanation of A.

B
Both A and R are true but R is not the correct explanation of A.

C
A is true but R is false.

D
A is false and R is also false.

Solution

Both statements are false. To increase the range of an ammeter, suitable low R (or shunt) should be connected in parallel to it. The ammeter with increased range has low resistance.
Question 9
1 / -0

Assertion (A): An electron has a high potential energy when it is at a location associated with a more negative value of potential, and a low potential energy when at a location associated with a more positive potential.

Reason (R):Electrons move from a region of higher potential to region of lower potential.

A
Both A and R are true and R is the correct explanation of A

B
Both A and R are true but R is not the correct explanation of A.

C
A is true but R is false.

D
A is false and R is also false.

Solution

Statements correct but reason is wrong because electrons move from a region of low potential to high potential.
Question 10
1 / -0

Assertion(A): A magnetic needle free to rotate in a vertical plane, orients itself (with its axis) vertical at the poles of the earth.

Reason (R): At the poles of the earth the horizontal component of earth’s magnetic field will be zero.

A
Both A and R are true and R is the correct explanation of A.

B
Both A and R are true but R is not the correct explanation of A.

C
A is true but R is false.

D
A is false and R is also false.

Solution

The given statement is correct and reason is the correct explanation of the above statement. At poles, magnetic needle orients itself vertically because horizontal components of earth’s field is zero there.
Question 11
1 / -0

Assertion(A): A proton and an electron, with same momenta, enter in a magnetic field in a direction at right angles to the lines of the force. The radius of the paths followed by them will be same.

Reason(R): Electron has less mass than the proton.

A
Both A and R are true and R is the correct explanation of A.

B
Both A and R are true but R is not the correct explanation of A.

C
A is true but R is false.

D
A is false and R is also false.

Solution

We know \(\frac{m\text v^2}r\) = Bqv sin \(\theta\) = Bqv \(\theta\)

Centripetal force = magnetic Lorentz force

sin \(\theta\) = sin \(90^{\theta}\) = 1 (\(\angle\) between \(\overrightarrow v \& \overrightarrow B=90^{\circ}\))

\(\frac{m\text v^2}r=Bq\text v\)

\(\frac{m\text v}r=Bq\)

\(r= \frac{mv}{Bq}=\frac{linear\,momentum}{Bq}\)

Since \(r=\frac{p}{Bq}\)

Given p, B are same

Also q for proton & electron is same except its sign

\(\therefore\) Radius is same. So first statement is correct but reason is not the correct explanation of the given assertion.
Question 12
1 / -0

Assertion (A): On Increasing the current sensitivity of a galvanometer by increasing the number of turns, may not necessarily increase its voltage sensitivity.

Reason(R ): The resistance of the coil of the galvanometer increases on increasing the number of turns.

A
Both A and R are true and R is the correct explanation of A

B
Both A and R are true but R is not the correct explanation of A.

C
A is true but R is false.

D
A is false and R is also false.

Solution

When we increase current sensitivity by increasing no. of turns, then resistance of coil also increases. So increasing current sensitivity does not necessarily imply that voltage sensitivity will increase because

\(V_g=\frac{I_g}R\)

\(\therefore\) if \(I_g\uparrow\&R\uparrow\) by different amounts, then \(V_g\) may increase or decrease.
Question 13
1 / -0

Which of the following statement is true?

A
Energy is created when a transformer steps up the voltage.

B
A transformer is designed to convert an AC voltage to DC voltage.

C
Step–up transformer increases the power for transmission.

D
Step–down transformer decreases the AC voltage.

Solution

Step down transformer decreases the ac voltage.
Question 14
1 / -0

If the secondary coil has a greater number of turns than the primary,

A
The voltage is stepped-up \((Vs >Vp )\) and arrangement is called a step-up transformer.

B
The voltage is stepped-down \((Vs<Vp)\) and arrangement is called a step-down transformer.

C
The current is stepped-up \((Is >Ip )\) and arrangement is called a step-up transformer.

D
The current is stepped-down \((Is <Ip )\) and arrangement is called a step- down transformer.

Solution

i.e. \(\frac{N_s}{N_p}=\frac{E_s}{E_p}\)

i.e. if no. of turns in secondary coil are more than no. of turns in primary, then voltage is increased or stepped up in secondary, so called step up transformer.
Question 15
1 / -0

We need to step-up the voltage for power transmission, so that

A
The current is reduced and consequently, the \(I^2R\) loss is cut down.

B
The voltage is increased, the power losses are also increased.

C
The power is increased before transmission is done.

D
The voltage is decreased so \(\frac{V^2}R\) losses are reduced.

Solution

Current is reduced if voltage is stepped – up so corresponding \(I^2R\) losses are cut down.
Question 16
1 / -0

A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns. The number of turns in the secondary in order to get output power at 230 V are

A
4

B
40

C
400

D
4000

Solution

Given \(E_i=2300V\)

\(E_0=230V\)

\(N_p=4000\)

\(N_s=?\)

\(\frac{E_i}{E_0}=\frac{N_p}{N_s}\)

\(\frac{2300}{230}=\frac{4000}{\text x}\)

x = 400 = \(N_s=\) No of turns in secondary coil.

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Mix Test - 9

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Mix Test - 9

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SHARING IS CARING

Question 1

Eddy currents are produced in the soft iron core of a transformer.

Electric Flux sharing is not properly done in primary and secondary coils.

Humming sound produed in the tranformers due to magnetostriction.

Primary coil is made up of a very thick copper wire.

Solution

Question 2

Electric field only

Drift speed and electric field

Electric field and current

Current only

Solution

Question 3

Decrease by 1%

Increased by 5%

Increased by 5%

Decrease by 4%

Solution

Question 4

\(2.512 \times 10^{-38} Am^2\)

\(1.256 \times 10^{-38} Am^2\)

\(0.628 \times 10^{-38} Am^2\)

Zero

Solution

Question 5

zero

3.125 volts

6.54 volts

16.74 volts

Solution

Question 6

39.70 kW

26.70 kW

13.35 kW

Zero

Solution

Question 7

Unaffected

Doubled

Halved

Quadrupled

Solution

Question 8

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false and R is also false.

Solution

Question 9

Both A and R are true and R is the correct explanation of A

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false and R is also false.

Solution

Question 10

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false and R is also false.

Solution

Question 11

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false and R is also false.

Solution

Question 12

Both A and R are true and R is the correct explanation of A

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false and R is also false.

Solution