12 ISC | PHYSICS | PREVIOUS YEAR QUESTIONS | UNIT 5 | ELECTROMAGNETIC WAVES |

 

UNIT 5 – ELECTROMAGNETIC WAVES

2025

1.     

(i) Name the electromagnetic wave travelling from the satellite to the dish antenna shown in the image above.

(ii) If the wavelength of an electromagnetic wave is 6 nm, what is its frequency?

2024

2.     (i) Name the electromagnetic radiation whose frequency is 10¹¹ Hz.

(ii) What is the speed of radio waves in vacuum?

2023

3.     (i) State how vectors E,B and c are oriented in an electromagnetic wave.

(ii) Name the electromagnetic wave/radiation which is used to study crystal structure.

2022

4.     Consider four electromagnetic radiations namely infrared radiations, ultraviolet radiations, micro waves and light. Which one of these has maximum frequency?

(a) infrared radiations             (b) ultraviolet radiations

(c) micro-waves                      (d) light

5.     Which one of the following is used to detect infrared radiations?

(a) Photocell                           (b) Fluorescent screen

(c) Ionization chamber           (d) Thermopile

6.     Which one of the following is used to study crystal structure of a crystalline salt?

(a) UV rays                             (b) X rays

(c) Micro-waves                     (d) Radio waves

7.     Relaxation time is

(a) the time interval between number of collisions of a free electron in a conductor.

(b) the average time interval between two successive collisions of a free electron with metallic ions in a conductor.

(c) the time interval between number of collisions of metal ions in a conductor.

(d) the time interval between collision of free electrons with each other

2020

8.     (i) State any one use of infrared radiations.

(ii) State any one source of ultraviolet radiations.

2019

9.     State any two properties of microwaves.

 

12 ISC | PHYSICS | PREVIOUS YEAR QUESTIONS | UNIT 4 | ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENT |

 

UNIT 4 – AC AND ELECTROMAGNETIC INDUCTION

2025

1.     Figure 3 below shows an ideal transformer. Explain why current flowing through secondary coil is greater than that in primary coil.

2.     Figure 9 shows a metallic rod AB of length l = 3 m moving in an (external uniform magnetic field, B =(1/π) T which is directed into the plane of this paper

 

If the position of the rod changes with time as x = πt, where x is in metre and t is in second, then:

(1) Calculate the motional emf developed in the rod.

(2) Name the law used to find the direction of induced current.

3.     When current flowing through a solenoid decreases from 15 A to 0 in 0.2 s, an emf of 30 V is induced in it. Calculate the coefficient of self-inductance of the solenoid.

4.     An alternating emf E = 5.0 sin (314 t) V is applied to a circuit containing a resistor connected in series with an unknown component X.

The current in the circuit is found to be I = 3.0 sin π (314t-π/3) A.

(a) Identify the component X.

(b) Calculate rms value (I_rms) of the current flowing through the circuit.

(c) Find the frequency of the source.

(d) Calculate power factor.

(e) Find the impedance (Z) of the circuit.

2024

5.     (i) What type of transformer is used in a mobile phone charger?

(ii) Why is the core of a transformer made of soft iron and not of steel?

6.     (a) A 220V, 50Hz ac source is connected to a coil having coefficient of self-inductance of 1 H and a resistance of 400Ω. Calculate: (1) the reactance of the coil. (2) the impedance of the coil. (3) the current flowing through the coil.

(b) Draw a labelled graph showing variation of impedance (Z) of a series LCR circuit Vs frequency (f) of the ac supply. Mark the resonant frequency as f₀.

7.     (a)When current flowing through a solenoid decreases from 5A to 0 in 20 milliseconds, an emf of 500V is induced in it.

(1) What is this phenomenon called?

(2) Calculate coefficient of self-inductance of the solenoid.

2023

8.     What is meant by “Motional emf”?

9.     When an electric current is passed through a wire or a coil, a magnetic field is produced. Is the reverse phenomenon possible i.e., can a magnetic field produce an electric current? Explain with the help of an appropriate example.

10.  A 60 Ω resistor, a 1.0 H inductor and a 4mF capacitor are connected in series to an ac supply generating an emf e = 300 sin (500t) V. Calculate: 

(a) impedance of the circuit.

(b) peak value of the current flowing through the circuit.

(c) phase difference between the current and the supply voltage.

11.  (a) An ac generator generates an emf which is given by e = 311 sin(240pt)V. Calculate:

(1) frequency of the emf.

(2) r.m.s. value of the emf.

12.  The primary coil of a transformer has 60 turns whereas its secondary coil has 3000 turns.

(1) If a 220V ac voltage is applied to the primary coil, how much emf is induced in the secondary coil?

(2) If a current of 5A flows in the primary coil, how much current will flow in a load in the secondary coil? State the assumption you have made regarding the transformer, in this calculation.

2022

13.  Two coils P and S are wound on a common core. Their coefficient of mutual inductance does not depend on:

(a) Number of turns in the coil P.

(b) Number of turns in the coil S.

(c) Material of the core.

(d) Voltage applied to the coil P or Q.

14.  Which one of the following statements is not true at resonance of a series LCR circuit?

(a) Reactance of the capacitor is equal to the reactance of the inductor.

(b) Impedance of the circuit is minimum

(c) Current in the circuit is minimum

(d) Current is in phase with supply voltage.

15.  A graph of reactance of capacitor Xc vs frequency (f) of an ac source is

16.  Consider a strong bar magnet NS and a solenoid AB as shown in Figure 3 below. G is a central zero galvanometer. Both the bar magnet and the solenoid are at rest.

The bar magnet is now moved slowly to the new position N’S’. The pointer of the galvanometer G

(a) remains undeflected at 0 mark.

(b) shows a constant deflection.

(c) shows a momentary deflection and comes back to zero.

(d) vibrates simple harmonically about 0 mark.

2020

17.  Write an expression for force per unit length between two long current carrying wires,kept parallel to each other, in vacuum and based on that define an ampere, the SI unit of current.

18.  Figure 1 below shows a metallic rod MN of length l = 80 cm, kept in a uniform magnetic field of flux density B – 0.5T, on two parallel metallic rails P and Q. Calculate the emf that will be induced between its two ends, when it is moved towards right with a constant velocity v = 36 km/hr.

19.  When current flowing through one coil changes from 0 Amp to 15 Amp in 0.2 s, an emf of 750 V is induced in an adjacent coil. Calculate the coefficient of mutual inductance of the two coils.

20.  (i) A 400W resistor, a 3H inductor and a 5μF capacitor are connected in series to a 220V, 50Hz ac source. Calculate the :

(1) Impedance of the circuit.

(2) Current flowing through the circuit.

(ii) Draw a labelled graph showing the variation of impedance (Z) of a series LCR circuit versus frequency (f) of the ac supply

21.  (i) When an alternating emf e = 310 sin (100πt) V is applied to a series LCR circuit, current flowing through the circuit can be given by i = 5 sin (100πt + π/3) A.

(1) What is the phase difference between the current and the emf ?

(2) Calculate the average power consumed by the circuit.

(ii) Obtain an expression for the resonant frequency (fo) of a series LCR circuit.

2019

22.  A transformer is used to step up an alternating emf of 200 V to 440 V. If the primary coil has 1000 turns, calculate the number of turns in the secondary coil.

23.  An alternating emf of 200 V, 50 Hz is applied to an L-R circuit, having a resistance R of 10 W and an inductance L of 0.05 H connected in series. Calculate:

(1) Impedance.

(2) Current flowing in the circuit.

(3) Draw a labelled graph showing the variation of inductive reactance (X_L) versus frequency (f)

2018

24.  An alternating emf of 220V is applied to a circuit containing a resistor R having resistance of 160Ω and a capacitor ‘C’ in series. The current is found to lead the supply voltage by an angle θ = tan^–1(3/4).

(i)              Calculate: (1) The capacitive reactance (2) Impedance of the circuit (3) Current flowing in the circuit

(ii)            If the frequency of the applied emf is 50 Hz, what is the value of the capacitance of the capacitor ‘C’?

25.  An A.C. generator generating an emf of e= 300 sin (100π t) V is connected to a series combination of 16 μF capacitor, 1H inductor and 100 Ω resistor. Calculate:

(i) Impedance of the circuit at the given frequency.

(ii) Resonant frequency ƒ₀.

(iii) Power factor at resonance frequency ƒ₀.

12 ISC | PHYSICS | PREVIOUS YEAR QUESTIONS | UNIT 3 | MAGNETISM |

 

UNIT 3 MAGNETISM

2025

1.     The relative permeability of substance ‘X’ is slightly less than one and that of substance ‘Y’ is slightly more than one. Then:

(a) ‘X’ is paramagnetic and ‘Y’ is ferromagnetic.

(b) ‘X’ is diamagnetic and ‘Y’ is ferromagnetic.

(c) ‘X’ is paramagnetic and ‘Y’ is diamagnetic.

(d) ‘X’ is diamagnetic and ‘Y’ is paramagnetic.

2.     A student has made connections, as shown in Figure 2 below, so that the wires MN and ST repel each other. But it is observed that they are attracting each other. What change should the student make for the wires to repel each other?

(a) Reverse the terminals of batteries E1 and E2.

(b) Reverse the terminals of battery E1 or E2.

(c) Choose supply voltage such that E1 = E2.

(d) Add key and ammeter to the circuit.

3.     Magnetic field at the centre of a circular coil is B. Calculate the magnetic field at the same point when each of the current, number of turns of the coil and its radius is doubled.

4.     A galvanometer having a resistance of 20 Ω shows a full scale deflection with a current of 1 mA. How can it be converted into a voltmeter with a range of 0–10 V?

5.     Two infinitely long straight wires PQ and RS carrying currents I₁ and I₂ respectively are kept 10 cm apart in vacuum. Calculate magnetic field (B) at the point X shown in Figure 8 below.

6.     An electron and a proton are moving along the +X axis. If an external magnetic field B = 0.314 T is applied along −Z axis: (a) What is the path followed by the electron due to the magnetic field? (b) Calculate the frequency of revolution of the proton.

2024

7.     Lorentz force in vector form is

8.     Assertion: When an electric current is passed through a moving coil galvanometer, its coil gets deflected.

Reason: A circular coil produces a uniform magnetic field around itself when an electric current is passed through it.

9.     Explain the meaning of the following statement: Curie temperature for soft iron is 770°C.

10.  Using Biot-Savart law, find out the expression for  magnetic flux density ‘B’, at the centre of a current carrying circular coil of radius R.

11.  Figure 4 below shows an infinitely long metallic wire YY’ which is carrying a current I’. P is a point at a perpendicular distance r from it.

(i)              What is the direction of magnetic flux density B of the magnetic field at the point P?

(ii)            What is the magnitude of magnetic flux density B of the magnetic field at the point P?

(iii)          Another metallic wire MN having length l and carrying a current I is now kept at the point P. If the two wires are in vacuum and parallel to each other, how much force acts on the wire MN due to the current I’ flowing in the wire YY’?

2023

12.  A circular coil has radius ‘r’, number of turn ‘N’ and carried a current ‘I’. Magnetic flux density ‘B’ at its centre is:

 

13.  A long straight wire AB carries a current of 5A. P is a proton travelling with a velocity of 2 × 10⁶ m/s, parallel to the wire, 0.2 m from it and in a direction opposite to the current, as shown in Figure 2 below. Calculate the force which magnetic field of the current carrying conductor AB exerts on the proton.

14.  A moving coil galvanometer of resistance 55 W produces a full scale deflection for a current of 250 mA. How will you convert it into an ammeter having a range of 0 – 3A?

15.  Using Ampere’s circuital law, obtain an expression for magnetic flux density ‘B’ at a point near an infinitely long and straight conductor, carrying a current I.

2022

16.  SI unit of magnetic dipole moment is:

(a) Am             (b) Am²           (c) Hm^–1          (d) Wbm^–2

17.  The point P is at a perpendicular distance of 0.2 m from a long straight wire YY’, which carries a current of 1.6 A, as shown in Figure 1 below.

Magnetic flux density of the magnetic field at point P is:

(a) 1.6 × 10^–6 T directed into the paper.

(b) 1.6 × 10^–6 T coming out of the paper.

(c) 0.8 × 10^–6 T directed into the paper.

(d) 0.8 × 10^–6 T coming out of the paper.

18.  A proton is moving in a uniform magnetic field B with a velocity v at an angle q with the field. The force acting on the proton is minimum when q is:

(a) 120°           (b) 90°             (c) 60°             (d) Zero

2019

19.  A rectangular loop of area 5 m² , has 50 turns and carries a current of 1 A. It is held in a uniform magnetic field of 0.1 T, at an angle of 30°. Calculate the torque experienced by the coil.

20.  An a.c. source of emf e = 200 sin ωt is connected to a resistor of 50Ω. Calculate: (1) Average current (Iavg). (2) Root mean square (rms) value of emf.

2018

21.  A circular coil carrying a current I has radius R and number of turns N. If all the three, i.e., the current I, radius R and number of turns N are doubled, then, magnetic field at its Centre becomes:

(a)   Double (c) Four times (b) Half (d) One fourth

22.  How will you convert a moving coil galvanometer into a voltmeter?

23.  A rectangular coil having 60 turns and area of 0.4 m2 is held at right angle to a uniform magnetic field of flux density 5×10^–5T. Calculate the magnetic flux passing through it.