List of top Questions asked in CBSE CLASS XII

At room temperature (27.0 °C) the resistance of a heating element is 100 Ω. What is the temperature of the element if the resistance is found to be 117 Ω, given that the temperature coefficient of the material of the resistor is \(1.70 \times 10^{-4} °C^{-1}.\)

A person with a normal near point(25cm)using a compound microscope with an objective of focal length 8.0mm and an eyepiece of focal length 2.5cm can bring an object placed at 9.0mm from the objective in sharp focus. What is the separation between the two lenses? Calculate the magnifying power of the microscope.

A compound microscope consists of an objective lens of focal length 2.0cm and an eyepiece of focal length 6.25cm separated by a distance of 15cm. How far from the objective should an object be placed in order to obtain the final image at(a)the least distance of distinct vision (25cm), and(b)at infinity? What is the magnifying power of the microscope in each case?

A manufacturer makes two types of toys A and B. Three machines are needed for this purpose and the time(in minutes)required for each toy on the machines is given below:
A manufacturer makes two types of toys
Each machine is available for a maximum 6 hours per day.If the profit on each toy of type A is Rs7.50 and that on each toy of type B is Rs5, show that 15 toys of type A and 30 toys of type B should be manufactured in a day to get maximum profit.

A long straight wire carries a current of 35 A. What is the magnitude of the field B at a point 20 cm from the wire?

A horizontal overhead power line carries a current of 90 A in east to west direction. What is the magnitude and direction of the magnetic field due to the current 1.5 m below the line?

A long straight wire in the horizontal plane carries a current of 50 A in north to south direction. Give the magnitude and direction of B at a point 2.5 m east of the wire.

A battery of emf 10 V and internal resistance 3 Ω is connected to a resistor. If the current in the circuit is 0.5 A, what is the resistance of the resistor? What is the terminal voltage of the battery when the circuit is closed?

The rate of a reaction quadruples when the temperature changes from \(293 \ K\) to \(313\  K\). Calculate the energy of activation of the reaction assuming that it does not change with temperature.

Differentiate the functions with respect to x.
\(sin(x^2+5)\)

Form the differential equation of the family of circles in the first quadrant which touch the coordinate axes.
In a box containing 100 bulbs, 10 are defective. The probability that out of a sample of 5 bulbs, none is defective is

The storage battery of a car has an emf of 12 V. If the internal resistance of the battery is 0.4Ω, what is the maximum current that can be drawn from the battery?

What is the de Broglie wavelength of
(a) a bullet of mass 0.040 kg travelling at the speed of 1.0 km/s,
(b) a ball of mass 0.060 kg moving at a speed of 1.0 m/s, and
(c)a dust particle of mass \(1.0×10^{–9}kg\) drifting with a speed of 2.2 m/s?
Light of frequency \(7.21×10^{14}Hz\) is incident on a metal surface. Electrons with a maximum speed of \(6.0×10^5 m/s\) are ejected from the surface.What is the threshold frequency for photoemission of electrons?

determine whether the given planes are parallel or perpendicular,and in case they are neither, find the angles between them. (a)7x+5y+6z+30=0 and 3x-y-10z+4=0 

(b)2x+y+3z-2=0 and x-2y+5=0 

(c)2x-2y+4z+5=0 and 3x-3y+6z-1=0 

(d)2x-y+3z-1=0 and 2x-y+3z+3=0 

(e)4x+8y+z-8=0 and y+z-4=0

The work function for a certain metal is 4.2 eV. Will this metal give photoelectric emission for incident radiation of wavelength 330 nm?

Double-convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 20 cm?

A beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12cm from P. At what point does the beam converge if the lens is(a)a convex lens of focal length 20cm, and(b)a concave lens of focal length 16cm?

What is the focal length of a convex lens of a focal length of 30cm in contact with a concave lens of a focal length of 20cm? Is the system a converging or a diverging lens? Ignore the thickness of the lenses.

From the relation \(R = R_0A^{\frac{1}{3}}\), where \(R_0\) is a constant and A is the mass number of a nucleus, show that the nuclear matter density is nearly constant (i.e. independent of A).

What is meant by 'disproportionation'? Give two examples of disproportionation reaction in aqueous solution.

 

The threshold frequency for a certain metal is \(3.3×10^{14} Hz\). If light of frequency \(8.2×10^{14} Hz\) is incident on the metal,predict the cut-off voltage for the photoelectric emission.
Compare the chemistry of actinoids with that of the lanthanoids with special reference to:
(i) electronic configuration (iii) oxidation state
(ii) atomic and ionic sizes and (iv) chemical reactivity.

Predict which of the following will be coloured in aqueous solution? Ti3+ ,V3+ , Cu+ , Sc3+ , Mn2+ , Fe3+ and Co2+ . Give reasons for each.