A wire of length \(L\) and radius \(r\) is clamped rigidly at one end. When the other end of the wire is pulled by a force \(f\), its length increases by \(l\). Another wire of same material of length \(2 L\) and radius \(2 r\) is pulled by a force \(2 f\). Then the increase in its length will be

For a certain metal, when monochromatic light of wavelength \(\lambda\) is incident, the stopping potential for photoelectrons is \(3V_0\). When the same metal is illuminated by light of wavelength \(2\lambda\), then the stopping potential becomes \(V_0\). The threshold wavelength for photoelectric emission for the given metal is \(\alpha\lambda\). The value of \(\alpha\) is _______.

An automobile, travelling at \(40\, km/h\), can be stopped at a distance of \(40\, m\) by applying brakes. If the same automobile is travelling at \(80\, km/h\), the minimum stopping distance, in metres, is (assume no skidding)..........\(m\)

The ratio of the power of a light source \(S_1\) to that the light source \(S_2\) is \(2 . S_1\) is emitting \(2 \times 10^{15}\) photons per second at 600 nm . If the wavelength of the source \(S_2\) is 300 nm , then the number of photons per second emitted by \(S_2\) is _______ \(\times 10^{14}\).

The magnetic moments associated with two closely wound circular coils \(A\) and \(B\) of radius \(r_A=10 cm\) and \(r_B=20 cm\) respectively are equal if: (Where \(N _A, I _{ A }\) and \(N _B, I _{ B }\) are number of turn and current of \(A\) and \(B\) respectively)

The typical transfer characteristic of a transistor in \(CE\) configuration is shown in figure. A load resistor of \(2\,k\Omega\) is connected in the collector branch of the circuit used. The input resistance of the transistor is \(0.50\,k \Omega\). The voltage gain of the transistor is.

Inside a uniform spherical shell \((a)\) the gravitational field is zero \((b)\) the gravitational potential is zero \((c)\) the gravitational field is same everywhere \((d)\) the gravitation potential is same everywhere \((e)\) all of the above Choose the most appropriate answer from the options given below

Three charged particle \(A, B\) and \(C\) with charges \(-4 q,  2 q\) and \(-2 q\) are present on the circumference of a circle of radius \(d\). the charged particles \(A, C\) and centre \(O\) of the circle formed an equilateral triangle as shown in figure. Electric field at \(O\) along \(x-\)direction is