Important Questions For Class XII Physics, Solved: Test Yourself From Past SQPs

The CBSE class XII examination is around the corner. Now is not the time to panic, but to focus. Concentrate on your studies, and you will definitely achieve your goal.?

At this time, constant revision of what you have studied is crucial.?

The following important physics class 12 questions have been taken from past sample questions papers of CBSE so, rest assured about the authenticity. The answers have been provided at the end.?

Q1. Find total energy stored in capacitors given in the circuit:
(2 marks)?

CBSE Class 12 Physics SQP 2019-20

Q2. A biconvex lens made of a transparent material of refractive index 1.25 is immersed in water of refractive index 1.33. Will the lens behave as a converging or a diverging lens? Justify your answer.
(2 marks)?

Q3. A heating element using nichrome connected to a 230 V supply draws an initial current of 3.2 A which settles after a few seconds to a steady value of 2.8 A. What is the steady temperature of the heating element if the room temperature is 27.0 °C and the temperature coefficient of resistance of nichrome is 1.70 × 10–4°C–1 ??

Q4. Suggest an idea to convert a full wave bridge rectifier to a half wave rectifier by changing the connecting wire/s. Draw the diagram and explain your answer.
(3 marks)?

Q5. Radiation of frequency 1015 Hz is incident on three photosensitive surfaces A, B and C. Following observations are recorded:Surface A: no photoemission occursSurface B: photoemission occurs but the photoelectrons have zero kinetic energy. Surface C: photo emission occurs and photoelectrons have some kinetic energy.Using Einstein’s photo-electric equation, explain the three observations.?

Q6. The total energy of an electron in the first excited state of the hydrogen atom is about –3.4 eV.
(3 marks)a. What is the kinetic energy of the electron in this state?b. What is the potential energy of the electron in this state?c. Which of the answers above would change if the choice of the zero of potential energy is changed?Ans7. formula K=-E , U = -2K (a) K = 3.4 eV & (b) U= -6.8 eV (c) The kinetic energy of the electron will not change. The value of potential energy and consequently, the value of total energy of the electron will change.?

Q7. a. Draw graphs showing the variations of inductive reactance and capacitive reactance with frequency of applied ac source.?

b. Draw the phasor diagram for a series LRC circuit connected to an AC source.?

c. When an alternating voltage of 220V is applied across a device X, a current of 0.25A flows which lags behind the applied voltage in phase by π/2 radian. If the same voltage is applied across another device Y, the same current flows but now it is in phase with the applied voltage.
(i) Name the devices X and Y.
(ii) Calculate the current flowing in the circuit when the same voltage is applied across the series combination of X and Y.
(5 marks)?

ANSWERS

Ans 1.

CBSE Class 12 Physics SQP 2019-20

Ans 2.

The value of (? – 1) is negative and ‘f’ will be negative. So it will behave like diverging lens.

Ans 3.

Given: V=230 V, I0= 3.2A, I=2.8A, ?0 =27 0C, α=1.70 × 10–4°C–1?

Using equation R =R0 (1+ α ?T)?

i.e V/ I = {V/ I0 } [1 + α ?T]?

and solving ?T= 840 , i.e. T = 840 + 27 = 867 0C?

Ans 4.

One possible answer: Change the connection of R from point C to point B. Now No Current flowing through D2 in the second half.

Ans 5.

From the observations made (parts A and B) on the basis of Einstein’s photoelectric equation, we can draw following conclusions:?

1. For surface A, the threshold frequency is more than 1015 HZ, hence no photoemission is possible.?

2. For surface B the threshold frequency is equal to the frequency of given radiation. Thus, photo-emission takes place but kinetic energy of photoelectrons is zero.?

3. For surface C, the threshold frequency is less than 1015 Hz. So photoemission occurs and photoelectrons have some kinetic energy.?

Ans 6.

formula K=-E , U = -2K?

(a) K = 3.4 eV &?

(b) U= -6.8 eV?

(c) The kinetic energy of the electron will not change. The value of potential energy and consequently, the value of total energy of the electron will change.??

Ans 7.

CBSE Class 12 Physics SQP 2023-24

CBSE Class 12 Physics SQP 2023-24

CBSE Class 12 Physics SQP 2023-24

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