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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 (Irms)
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 (XL) 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.
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