# The half-life of a radioactive substance is $$20$$ minutes. In how much time, the activity of substance drops to $$(\frac{1}{16})^{\mathrm{th}}$$ of its initial value? 1. $$80$$ minutes 2. $$20$$ minutes 3. $$40$$ minutes 4. $$60$$ minutes

Subtopic:  Radioactivity (OLD NCERT) |
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The net magnetic flux through any closed surface is:
1. negative
2. zero
3. positive
4. infinity
Subtopic:  Analogy between Electrostatics & Magnetostatics |
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A metal wire has mass $$(0.4\pm 0.002)~\mathrm{g}$$, radius $$(0.3\pm 0.001)~\mathrm{mm}$$ and length $$(5\pm 0.02)~\mathrm{cm}$$. The maximum possible percentage error in the measurement of density will nearly be:
1. $$1.4 \%$$
2. $$1.2 \%$$
3. $$1.3 \%$$
4. $$1.6 \%$$
Subtopic:  Errors |
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The angular acceleration of a body, moving along the circumference of a circle, is:
 1 along the axis of rotation 2 along the radius, away from centre 3 along the radius towards the centre 4 along the tangent to its position
Subtopic:  Rotational Motion: Kinematics |
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The magnetic energy stored in an inductor of inductance $$4~\mathrm{\mu H}$$ carrying a current of $$2~\text{A}$$ is:
1. $$8~\mathrm{\mu J}$$
2. $$4~\mathrm{\mu J}$$
3. $$4~\mathrm{mJ}$$
4. $$8~\mathrm{mJ}$$
Subtopic:  Self - Inductance |
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A full wave rectifier circuit consists of two $$\mathrm{p\text-n}$$ junction diodes, a centre-tapped transformer, capacitor and a load resistance. Which of these components remove the ac ripple from the rectified output?
 1 load resistance 2 a centre-tapped transformer 3 $$\mathrm{p\text-n}$$ junction diodes 4 capacitor
Subtopic:  Rectifier |
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A football player is moving southward and suddenly turns eastward with the same speed to avoid an opponent. The force that acts on the player while turning is:
 1 along south-west 2 along eastward 3 along northward 4 along north-east
Subtopic:  Newton's Laws |
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The work functions of Caesium $$(\mathrm{Cs})$$, Potassium $$(\mathrm{K})$$ and Sodium $$(\mathrm{Na})$$ are $$2.14~\text{eV}$$, $$2.30~\text{eV}$$ and $$2.75~\text{eV}$$ respectively. If incident electromagnetic radiation has an incident energy of $$2.20~\text{eV}$$. which of these photosensitive surfaces may emit photoelectrons?
 1 $$\mathrm{Na}$$ only 2 $$\mathrm{Cs}$$ only 3 Both $$\mathrm{Na}$$ and $$\mathrm{K}$$ 4 $$\mathrm{K}$$ only
Subtopic:  Photoelectric Effect: Experiment |
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If $$\oint_s \vec{E} \cdot \overrightarrow{d S}=0$$ over a surface, then:

 1 the electric field inside the surface is necessarily uniform. 2 the number of flux lines entering the surface must be equal to the number of flux lines leaving it. 3 the magnitude of electric field on the surface is constant. 4 all the charges must necessarily be inside the surface.
Subtopic:  Gauss's Law |
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Given below are two statements:
 Statement I: Photovoltaic devices can convert optical radiation into electricity. Statement II: Zener diode is designed to operate under reverse bias in the breakdown.

 1 Statement I is False but Statement II is True. 2 Both Statement I and Statement II are True. 3 Both Statement I and Statement II are False. 4 Statement I is True but Statement II is False.
Subtopic:  Applications of PN junction |
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