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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