Physics Test 174

Result

Physics Test 174

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Question 1
4 / -1

The equivalent resistance between A and B will be (in ?)

A
2/7

B
8

C
4/3

D
7/3

Solution

As C & D are at same potential by symmetry of circuit °

It is balanced wheat-stone bridge Hence the circuit has equivalant resistance 7/3 Ω
Question 2
4 / -1

As shown in figure, a permanent magnet and current carrying coil are placed. If the coil is moved towards magnet, then current in coil (Magnet is symmetrical) :

A
increases

B
decreases

C
remains same

D
first increases then decreases

Solution

No change in the flux occurs due to the described motion of the magnet. Hence no current will be induced in the coil.
Question 3
4 / -1

A
current will flow from A to B

B
current may flow from A to B

C
current will flow from B to A

D
the direction of current will depend on r.

Solution

Current through resistance woll be from

A to B if

20 – ε > 2 ⇒ ε < 18

and from

B to A if 20 – ε < 2
Question 4
4 / -1

A super conducting loop having an inductance 'L' is kept in a magnetic field which is varying with respect to time. If is the total flux, e = total induced emf, then:

A
φ = constant

B
I = 0

C
ε ≠ 0

D
None of these

Solution
Question 5
4 / -1

A battery of internal resistance ' r ' and e.m.f. ε is connected to a variable external resistor AB. If the sliding contact is moved from A to B, then terminal potential difference of battery will :

A
remain constant & is independent of value of external resistance

B
increase continuously

C
decrease continuously

D
first increase and then will decrease.

Solution

V = E - i r. Now, if we go from A → B, then resistance of the circuit increases, ' i ' decreases

∴ V increases
Question 6
4 / -1

Figure shows a conducting horizontal rod of resistance r is made to oscillate simple harmonically with a fixed amplitude in a uniform and constant magnetic field B, directed inwards. The ends of rod always touch two parallel fixed vertical conducting rails. The ends of rails are joined by an inductor and a capacitor having self inductance and capacitance 1/π Henry and 1/π farad respectively. The amplitude of current in the circuit depends on the frequency of oscillation of rod. The amplitude of the current will be maximum when the time period of rod is : (do not consider self inductance anywhere other than in the inductor)

A
0.5 sec

B
1 sec

C
2 sec

D
4 sec

Solution

Here oscillating rod is an AC source because emf induced in it is (vBℓ) ; which varies sinusoidally because v varies sinusoidally.

Maximum current will flow through the circuit under resonance condition. Therefore time period of oscillation of rod is
Question 7
4 / -1

In the figure shown the equivalent capacitance between 'A' and 'B' is :

A
3.75 F

B
2 F

C
21 F

D
16 F

Solution
Question 8
4 / -1

A very small circular loop of area 5 × 10^–4 m² and resistance 2 ohm is initially concentric and coplanar with a stationary loop of radius 0.1 m. If one ampere constant current is passed through the bigger loop and the smaller loop is rotated about its diameter with constant angular velocity ω. The current induced (in ampere) in the smaller loop will be :

A

B
πω x 10^-9 cosωt

C

D
πω x 10^-9 sinωt

Solution
Question 9
4 / -1

The capacitor shown in figure 1 is charged completely by connecting switch S to contact a. If switch S is thrown to contact b at time t = 0, which of the curves in figure 2 above represents the magnitude of the current through the resistor R as function of time t ?

A
J

B
K

C
L

D
M

Solution

The potential difference across completely charged capacitor is V. As the switch is pushed to b, the initial current in the resistor R is V/R. Hence J is the correct curve.
Question 10
4 / -1

At a given instant the current and self induced emf in an inductor are directed as shown in figure. If the induced emf is 17 volt and rate of change of current is 25 kA/s the correct statement is :

A
Current is increasing and inductance of coil is 3.4 μH

B
Current is decreasing and inductance of coil is 680 μH

C
Current is decreasing and inductance of coil is 3.4 μH

D
Current is increasing and inductance of coil is 6.8 μH

Solution