Science (English Medium) Class 12 - CBSE Question Bank Solutions

Light of wavelength 2000 Å falls on a metal surface of work function 4.2 eV.

What is the kinetic energy (in eV) of the fastest electrons emitted from the surface?

Light of wavelength 2000 Å falls on a metal surface of work function 4.2 eV.

What will be the change in the energy of the emitted electrons if the intensity of light with same wavelength is doubled?

Light of wavelength 2000 Å falls on a metal surface of work function 4.2 eV.

If the same light falls on another surface of work function 6.5 eV, what will be the energy of emitted electrons?

A test charge q is made to move in the electric field of a point charge Q along two different closed paths (Figure). First path has sections along and perpendicular to lines of electric field. Second path is a rectangular loop of the same area as the first loop. How does the work done compare in the two cases?

Two cells of emf’s approximately 5V and 10V are to be accurately compared using a potentiometer of length 400 cm.

First a set of n equal resistors of R each are connected in series to a battery of emf E and internal resistance R. A current I is observed to flow. Then the n resistors are connected in parallel to the same battery. It is observed that the current is increased 10 times. What is ‘n’?

A metal plate is getting heated. It can be because ______.

1. a direct current is passing through the plate.
2. it is placed in a time varying magnetic field.
3. it is placed in a space varying magnetic field, but does not vary with time.
4. a current (either direct or alternating) is passing through the plate.

Consider a metallic pipe with an inner radius of 1 cm. If a cylindrical bar magnet of radius 0.8 cm is dropped through the pipe, it takes more time to come down than it takes for a similar unmagnetised cylindrical iron bar dropped through the metallic pipe. Explain.

When a voltage measuring device is connected to AC mains, the meter shows the steady input voltage of 220V. This means ______.

The output of a step-down transformer is measured to be 24 V when connected to a 12-watt light bulb. The value of the peak current is ______.

A neutron beam of energy E scatters from atoms on a surface with a spacing d = 0.1 nm. The first maximum of intensity in the reflected beam occurs at θ = 30°. What is the kinetic energy E of the beam in eV?

In a npn transistor circuit, the collector current is 10 mA. If 95 per cent of the electrons emitted reach the collector, which of the following statements are true?

1. The emitter current will be 8 mA.
2. The emitter current will be 10.53 mA.
3. The base current will be 0.53 mA.
4. The base current will be 2 mA.

In a CE transistor amplifier there is a current and voltage gain associated with the circuit. In other words there is a power gain. Considering power a measure of energy, does the circuit voilate conservation of energy?

In the circuit shown in figure, find the value of R_C.

Would sky waves be suitable for transmission of TV signals of 60 MHz frequency?

Assertion(A): The photoelectrons produced by a monochromatic light beam incident on a metal surface have a spread in their kinetic energies.

Reason(R): The energy of electrons emitted from inside the metal surface, is lost in collision with the other atoms in the metal.

The short wavelength limit for the Lyman series of the hydrogen spectrum is 913.4 Å. Calculate the short wavelength limit for the Balmer series of the hydrogen spectrum.

A narrow slit is illuminated by a parallel beam of monochromatic light of wavelength λ equal to 6000 Å and the angular width of the central maximum in the resulting diffraction pattern is measured. When the slit is next illuminated by light of wavelength λ’, the angular width decreases by 30%. Calculate the value of the wavelength λ’.

Two cells of emfs E₁ and E₂ and internal resistances r₁ and r₂ respectively are connected in parallel as shown in the figure. Deduce the expression for the

1. equivalent emf of the combination
2. equivalent internal resistance of the combination
3. potential difference between the points A and B.

Two large, thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs and of magnitude 17.7 × 10^–22 C/m². What is electric field intensity E:

1. in the outer region of the first plate, and
2. between the plates?