BOARD MODEL TEST – 2023-24

Name of the Student: ___________________________ Date : 16/09/2023

Grade/Section : XII-Stalwarts/Titans/Pioneers Subject : PHYSICS
Time/Duration: 1 ½ Hrs Total Marks : 35
Signature of the Invigilator : ______________
SECTION – A
I. Choose the Correct Answers: [09 X 1M = 09M]
 
1. A test charge of 1.6 1019 C is moving with a velocity v  4i  3k ms 1 in a magnetic field B  3k  4i T .
   
The force on this test charge is
a) 24 j N b) 24 j N c) 24k N d)0
2. A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field B.
The work done to rotate the loop by 30° about an axis perpendicular to its plane is
MB MB
a)MB b) 3 c) d)zero
2 2
3. The strength of magnetic field at the centre of circular coil is

0 I  1  0 I 0 I  1  0 I  1 
a) 1   b) c) 1   d) 1  
R   R 2R    2R   
4. Three long, straight parallel wires, carrying current are arranged as shown in the figure. The force
experienced by a 25 cm length of wire C is

a) 103 N b) 2.5  103 N c)zero d) 1.5 103 N

5. A current I is flowing through the loop as shown in the figure. ( MA  R, MB  2 R) . The magnetic field at the centre
0 I
of the loop is times.
R

5 5
a) , into the plane of the paper b) , out of the plane of the paper
16 16
7 7
c) , out of the plane of the paper d) , into the plane of the paper
16 16
6. If a charged particle moves through a magnetic field perpendicular to it
(a) both momentum and energy of particle change. (b) momentum as well as energy are constant.
(c) energy is constant but momentum changes. (d) momentum is constant but energy changes.

7. An electron is projected with velocity V along the axis of a current carrying long solenoid. Which one of the
following Statements is true?
(a) The path of the electron will be circular about the axis. (b) The electron will be accelerated along the axis.
(c) The path of the electron will be helical

(d) The electron will continue to move with the same velocity V along the axes of the solenoid
8. Assertion : When coil is suspended in a radial magnetic field, it experiences a maximum torque
Reason : The torque tends to rotate the coil on its own axis.
a) both A and R are true and R is the correct explanation of A.
b) both A and R are true but R is NOT the correct explanation of A. c) A is true but R is false.
 d) A is false and R is also false.
9. Assertion : When radius of circular loop carrying current is doubled, its magnetic moment becomes four times.
Reason : Magnetic moment depends on the area of the loop
SECTION - B
II. Answer the following questions [3 X 2M = 6M]
10. An electron and a proton moving with the same speed enter the same magnetic field region at right angles
to the direction of the field. For which of the two particles will the radius of circular path be smaller?
11. State the law used to determine the direction of magnetic field at the centre of current carrying circular Coil.
12. Two long and parallel straight wires A and B carrying currents of 8.0 A and 5.0 A in the same direction are separated by a
distance of 4.0 cm. Estimate the force on a 10 cm section of wire A.
(Or)
A galvanometer coil has a resistance of 15 Ω and the metre shows full scale deflection for a current of 4 mA. How will you
convert the meter into an ammeter of range 0 TO 6A?
SECTION – C
III. Answer the following questions [2 X 3M = 6M]
13. Describe the path of a charged particle moving in a uniform magnetic field with initial velocity
(i) parallel to (or along) the field. (ii) perpendicular to the field. (iii) at an arbitrary angle θ(0° < θ < 90°).
14. A long straight wire, of circular cross-section of radius a carries a steady current I. The current is uniformly
distributed across the cross section. Apply ampere’s circuital law to calculate the magnetic field at a point
r in the region for (i) r<a and (ii) r> a. Plot a graph showing the nature of this variation. (OR)
A wire AB is carrying a steady current of 12 A and is lying on the table. Another wire CD carrying 5 A is
held directly above AB at a height of 1mm. Find the mass per unit length of the wire CD so that it remains
suspended at its position when left free. Give the direction of the current flowing in CD with respect to that in
AB. [ take the value of g=10 ms 2 ] SECTION – D
III. Answer the following Case study questions [1 X 4M = 4M]
15. A galvanometer is a device which is used to detect presence of current in a conductor. But it cannot be used
directly as an ammeter. It has a very large resistance. If connected in series like an ammeter, it affects the
value of current in a circuit. But it can be converted into an ammeter. Similarly, a galvanometer can be used as
a voltmeter also. In both cases, a shunt resistance is connected with the galvanometer.
(i) To convert a galvanometer of resistance RG into voltmeter a shunt resistance R is connected.
(a) in parallel so that R =  V  R (b) in series so that R  V  R
G G
Ig Ig
RG I g
(c) in parallel so that R  (d) in series so that R  RG I g
I  Ig I  Ig
(ii) To convert a galvanometer of resistance RG into ammeter a shunt resistance R is connected.
(a)in parallel so that R  V  RG (b) in series so that R  V  RG (c)in parallel so that R  RG I g
Ig Ig I  Ig
RG I g
(d) in series so that R 
I  Ig
(iii) Why is galvanometer not used directly as ammeter?
(a) It gives full scale deflection for even small current values. (b) It has high resistance.
(c) It is always connected in parallel while ammeter is connected in series. (d) Both (a) and (b)
(iv) A galvanometer with coil of resistance 120 shows full scale deflection for current of 2.5 mA. To convert it
into an ammeter of range 0-7.5 A, we connect a shunt resistance
(α) 0.04 Ω (b) 0.08 Ω (c) 0.12 Ω (d) 0.16 2
(v) The reading of current measured by ammeter is
(a) equal to actual current. b) slightly less than actual current. c) slightly more than actual current. d) zero.
SECTION – E
IV. Answer the following questions [2 X 5M = 10M]
16. (a) State Biot-Savart’s law and express this law in the vector form
(b) Two identical circular coils P and Q each of radius R, carrying currents I A and 3A respectively, are placed
concentrically and perpendicular to each other lying in the XY and YZ planes. Find the magnitude and
direction of the net magnetic field at the centre of the coils.
17. Derive the expression for force per unit length between two long straight parallel current carrying
conductors. Hence, define one ampere.