Physics Test

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Physics Test - 26

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Question 1
4 / -1

For a transistor, the current amplification factor is 0.8. If the transistor is in common emitter configuration and the base current changes by 6 mA, the change in the collector current is

A
6 mA

B
4.8 mA

C
24 mA

D
8 mA

Solution

\(\alpha=\frac{I_{0}}{I_{E}}\)
\(0.8 \mathrm{I}_{\mathrm{E}}=\mathrm{I}_{\mathrm{C}}\)
Here,
\(\mathrm{I}_{\mathrm{E}}=\mathrm{I}_{\mathrm{C}}+\mathrm{I}_{\mathrm{B}}\)
\(0.8 \mathrm{I}_{\mathrm{B}}=0.2 \mathrm{I}_{\mathrm{C}}\)
\(4 \mathrm{I} \mathrm{B}=\mathrm{I}_{\mathrm{C}}\)
\(4 \Delta \mathrm{I}_{\mathrm{B}}=\Delta \mathrm{l}_{\mathrm{C}}\)
\(4 \times 6 \mathrm{mA}=\Delta \mathrm{l}_{\mathrm{C}}\)
\(\Delta \mathrm{I}_{\mathrm{C}}=24 \mathrm{m} \mathrm{A}\)
Question 2
4 / -1

Three identical bulbs connected in series dissipate a power p. If the bulbs are connected in parallel, the power dissipated will be

A
p/3

B
3p

C
9p

D
p/9

Solution

When three bulbs are connected in series, then power consumed \(\frac{1}{p}=\frac{1}{p_{1}}+\frac{1}{p_{2}}+\frac{1}{p_{3}}\)
Or \(\frac{1}{p}=\frac{3}{p^{\prime}}\) or \(p=\frac{p^{\prime}}{3}\)
p is the individual power of a bulb but when bulbs are connected in parallel, then power is \(\mathrm{p}^{\prime}+\mathrm{p}^{\prime}+\mathrm{p}^{\prime}=3 \mathrm{p}^{\prime},\) or \(9 \mathrm{p}\)
So, \(3^{\text {rd }}\) option is the correct answer.
Question 3
4 / -1

A body moving along the circular path of radius `R` describes an angle of 60o at the center of the circle, while moving from A to B. The displacement of the body is

A
R/2

B
R

C
√3R

D
√2R

Solution

Coordinates of center \(=(0,0)\) Coordinates of \(\mathrm{A}\left(\mathrm{X}_{\mathrm{a}}, \mathrm{Y}_{\mathrm{a}}\right)=(0, \mathrm{R})\)
Coordinates of \(\mathrm{B}\left(\mathrm{X}_{\mathrm{b}}, \mathrm{Y}_{\mathrm{b}}\right)=(\mathrm{R} \cos , \mathrm{R} \sin )=\left(\mathrm{R} \cos 60^{\circ}, \mathrm{R} \sin 60^{\circ}\right)=(\mathrm{R} / 2, \mathrm{R} / 2)\)
Displacement \(\mathrm{AB}=\left[\left(x_{B}-x_{A}\right)^{2}+\left(y_{B}-y_{A}\right)^{2}\right]^{\frac{1}{2}}\)
\(=\left[\left(\frac{R}{2}-R\right)^{2}+\left(\frac{\sqrt{3} R}{2}-0\right)^{2}\right]^{\frac{1}{2}}\)
\(=\left[\frac{R^{2}}{4}+\frac{3 R^{2}}{4}\right]^{\frac{1}{2}}=R\)
Or we can use the concept of equilateral triangle, as two sides are same in this case
the angles made by the OA and \(O B\) with \(A B\) will be \(60^{\circ}\) hence displacement will be \(R\)
Question 4
4 / -1

An alien is celebrating his 4^thbirthday on his home planet, which is at a distance of 4 AU from the sun. What is the age of the alien in terrestrial years?

A
1 year

B
16 years

C
32 years

D
None of these

Solution

\(\frac{T_{1}^{2}}{T_{2}^{2}}=\frac{R_{1}^{3}}{R_{2}^{3}} \Rightarrow \frac{T_{1}^{2}}{T_{2}^{2}}=\frac{1^{3}}{4^{3}}\)

\(\Rightarrow T_{2}=8 T_{1}\)

Hence, age of the alien in terms of terrestrial years T2 = 8 x 4 = 32 years
Question 5
4 / -1

The value of 2⁵ in octal system is

A
40

B
50

C
200

D
400

Solution

2⁵= (32)10
(32)₁₀ = (40)₈
Question 6
4 / -1

In a given circuit, the heat produced in a \(5 \Omega\) resistor due to the current flowing through it is \(10 \mathrm{J}-5^{-1}\). The heat
generated in the \(4 \Omega\) resistor is:

A
4 Js^-1

B
1.6 Js^-1

C
2 Js^-1

D
8 Js^-1

Solution

The potential difference across the combination of \(6 \Omega\) and \(4 \Omega\) resistance is same as that across \(5 \Omega\) resistance.
\[
P=\frac{V^{2}}{R}
\]
Given, \(\quad P=10 \mathrm{J}-\mathrm{s}^{-1}, R=5 \Omega\)
\(\therefore \quad V^{2}=10 \times 5=50\)
\(\Rightarrow \quad V=\sqrt{50}\) volt
The \(4 \Omega\) and \(6 \Omega\) resistors are connected in series, hence current across them is same. Also, \(V=i R\)
\[
\sqrt{50}=i\left(R_{1}+R_{2}\right)=i(6 \Omega+4 \Omega)
\]
\(\Rightarrow \quad i=\frac{\sqrt{50}}{10} \mathrm{A}\)
Heat generated in \(4 \Omega\) resistor is
\[
P=i^{2} R=\frac{50}{100} \times 4=2 J-s^{-1}
\]
Question 7
4 / -1

Directions: In the following question, a statement of Assertion is given, followed by a corresponding statement of Reason. Mark the correct answer as:
(a) If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
(b) If both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.
(c) If Assertion is true, but Reason is false.
(d) If both Assertion and Reason are false.
Assertion: The earth is slowing down and as a result the moon is coming nearer to it.
Reason: The angular momentum of the earth-moon system is not conserved.

A
(a)

B
(b)

C
(c)

D
(d)

Solution

Planetary motions can exist only if they obey the law of conservation of angular momentum. If this law is violated, then no gravitational law will be able to explain the behaviour of the planets and the satellites.
Question 8
4 / -1

The figure shows three spherical and equipotential surfaces A, B and C around a point charge q. The potential difference V_A - V_B = V_B - V_C. If t₁ and t₂ are the distances between them, then

A
t₁ = t₂

B
t₁> t₂

C
t₁ < t₂

D
No relation between t₁& t₂

Solution
Question 9
4 / -1

Two rods A and B of different materials are welded together, as shown in the figure. If their thermal conductivities are K₁ and K₂, then the thermal conductivity of the composite rod will be

A
(K₁+ K₂)

B
(K₁ + K₂)/2

C
\(\frac{1}{K}=\frac{1}{K_{1}}+\frac{1}{K_{2}}\)

D
\(\frac{2 K_{1} K_{2}}{K_{1}+K_{2}}\)

Solution
Question 10
4 / -1

Consider the following two statements A and B, and identify the correct answer.
A: During amplification, the frequency of the signal is increased.
B: The voltage gain is more in common base transistor amplifier than in common emitter transistor amplifier.

A
Both A and B are true.

B
A is true, but B is false.

C
A is false, but B is true.

D
Both A and B are false.

Solution

Both the given statements are false, so \(4^{\text {th }}\) option is the answer. \(24 \beta=\left(\frac{\Delta / C}{\Delta / B}\right)_{V_{c}=}\)
This is the definition of current gain.

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Physics Test - 26

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Physics Test - 26

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Question 1

6 mA

4.8 mA

24 mA

8 mA

Solution

Question 2

p/3

3p

9p

p/9

Solution

Question 3

R/2

R

√3R

√2R

Solution

Question 4

1 year

16 years

32 years

None of these

Solution

Question 5

40

50

200

400

Solution

Question 6

4 Js-1

1.6 Js-1

2 Js-1

8 Js-1

Solution

Question 7

(a)

(b)

(c)

(d)

Solution

Question 8

t1 = t2

t1 > t2

t1 < t2

No relation between t1 & t2

Solution

Question 9

(K1 + K2)

(K1 + K2)/2

\(\frac{1}{K}=\frac{1}{K_{1}}+\frac{1}{K_{2}}\)

\(\frac{2 K_{1} K_{2}}{K_{1}+K_{2}}\)

Solution

Question 10

Both A and B are true.

A is true, but B is false.

A is false, but B is true.

Both A and B are false.

Solution

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4 Js^-1

1.6 Js^-1

2 Js^-1

8 Js^-1

t₁ = t₂

t₁> t₂

t₁ < t₂

No relation between t₁& t₂

(K₁+ K₂)

(K₁ + K₂)/2