Physics-7. UNIT–15 TEST

UNIT–15 TEST 1. Two long parallel wires P and Q are held perpendicular to the plane of the paper with a distance of 5 m between them. If P and Q carry current of 2.5 amp and 5 amp reactively in the same direction, then the magnetic field at a point half-away between the wires is: (A) (B) (C) (D) 2. A galvanometer has resistance of 7 and gives a full scale deflection for a current of 1.0 A. How will you convert it into a voltmeter of range 10V? (A) 3 in series (B) 3 in parallel (C) 17 in series (D) 30 in series 3. An infinitely long straight conductor is bent into the shape as shown in figure. It carries a current i ampere and the radius of the circular loop is r meter. Then the magnetic induction at the centre of the circular part is (A) Zero (B) (C) (D) 4. A charged particle is projected in a plane perpendicular to a uniform magnetic field. The area bounded by the path described by the particle is proportional to (A) The velocity (B) The momentum (C) the kinetic energy (D) none of these 5. The vector form of Biot-Savart Law for a current carrying element is: (A) (B) (C) (D) None of these 6. An electron accelerated by 200V, enters a magnetic field. If its velocity in 8.4x106 m/sec. then (e/m) for it will be: (in C/kg) (A) 1.75 x 1010 (B) 1.75 x 1011 (C) 1.75 x 109 (D) 1.75 x 106 7. Two particles accelerated with same voltage enter a uniform magnetic field perpendicularly. The radius if the circular paths are and the charge on particles is same, the ratio of (A) (B) (C) (D) 8. Length of two wires is 0.5 m and distance between the wires is 1 m. If 1 amp current is passed in the wires force per unit length between the wires is: (A) 4 x 10–7 N/m (B) 2 x 10–7 N/m (C) 10–7 N/m (D) none 9. Specific charge on a proton is 9.6x107 C/Kg. A proton is moving in a magnetic field of IT in circular path of 0.5 m radius. The energy of proton in MeV is: (A) 16.34 (B) 12.02 (C) 8.25 (D) 4.84 10. Magnetic field due to a straight current carrying wire is 10–5 T at a distance of 10 cm. The current in the wire is : (A) 0.40 amp (B) 5 amp (C) 12.6 amp (D) 25.1 amp 11. A galvanometer has resistance G and a current flowing in it produces full scale deflection. is the value of the shunt, which converts it into an ammeter of range O-I and is the value of the shunt for the range O-2I. The ratio is : (A) (B) (C) 2 (D) 1 12. An electron of mass and a proton of mass are injected into a uniform magnetic field at right angles to the direction of the field, with equal velocity. The ratio of the radii of their orbits is equal to : (A) 1 (B) (C) 2 (D) 13. With a resistance R connected in series with a galvanometer of resistance 100 , if acts as a voltmeter of range 0-V. To double the range a resistance of 1000 is to be connected in series with R. Then the value of R is: (A) 1100 (B) 800 (C) 900 (D) 1000 14. Electron of mass m charge e is travelling with a speed along a circular path of radius r at right angles to uniform magnetic field B. If the speed of the electron i doubled and the magnetic field is halved the resulting path would have a radius (A) (B) (C) 2r (D) 4r 15. The strength of the magnetic field at a point distant r near a long straight current carrying wire is B. The field at a distance r/2 will be (A) B/2 (B) B/4 (C) 4B (D) 2B 16. A Proton enters a magnetic field with velocity parallel to the magnetic field. The path followed by the proton is a (A) circle (B) parabola (C) helix (D) straight line 17. Current I is carried in a wire of length L. If the wire is formed into a circular coil, the maximum magnitude of torque in a given magnetic field B, will be : (A) (B) (C) (D) 18. An electron is moving with velocity in a direction parallel to a magnetic field . The magnitude of force acting on the electron will be (A) Zero (B) e ( . ) (C) e ( x ) (D) none 19. A Coil of radius 10cm and 50 turns carries a current of 5A. Magnetic induction at its centre is - (A) 1 mT (B) 1.57 mT (C) 2 mT (D) 3.14 mT 20. Two particles X and Y, having equal charges after being accelerated through the same potential difference, enter a region of uniform magnetic field and describe circular paths of radii and reactively. The ratio of mass X to mass of Y is - (A) (B) (C) (D) 21. Due to the flow of current in a circular loop of radius R. the magnetic induction produced at the centre of the loop is B. The magnetic moment of the loop is [ = Permeability constant]: (A) (B) (C) (D) 22. A circular loop of radius 0.0157 m carries a current of 2.0 amp. The magnetic field at the centre of the loop is (A) 1.57 x 10–5 weber/m2 (B) 8.0 x 10–5 weber/m2 (C) 2.5 x 10–5 weber/m2 (D) 3.14 x 10–5 weber/m2 23. The dimensions of magnetic field are (A) ML0T–2I–1 (B) ML0T–1Q–1 (C) MLT–1I–2 (D) MLT–2Q–1 24. The dimensions of magnetic permeability are (A) ML-1T–1I–1 (B) MLT–2I–2 (C) MLTQ–1 (D) MLT0Q–2 25. The magnetic field of a current carrying coil of radius r at a distance (>>r) from the centre of the coil varies as (A) (B) (C) (D) 26. A circular coil has 250 turns and a mean diameter of 20 cm. It carries a current of 5A. What is the strength of the magnetic field at a point on its axis at a distance of 5 m from the centre of the coil? (A) 4 x 10–7 T (B) 2 x 10–7 T (C) 4 x 10–8 T (D) 2 x 10–8 T 27. The sensitivity of a moving coil galvanometer depends on (A) angle of deflection (B) earth's magnetic field (C) moment of inertia of the coil (D) none of the above 28. A straight wire carrying a current 10 A is bent into a semicircular are of radius 5 cm as shown. The magnetic of magnetic field at the centre is (A) 1.5 x 10–5 T (B) 3.14 x 10–5 T (C) 6.28 x 10–5 T (D) 19.6 x 10–5 T 29. A long straight wire carries an electric current of 2 A. the magnetic induction at a perpendicular distance of 5m from the wire will be (A) 4 x 10–8 T (B) 8 x 10–8 T (C) 12 x 10–8 T (D) 16 x 10–8 T 30. An electron remains undeflected when passing perpendicular to mutually perpendicular electric and magnetic fields. If the magnetic field is 8 Gauss and the electric field is 4000 V/m, the velocity of the electron is (A) 2 x 106 m/s (B) 5.0 x 106 m/s (C) 6 x 106 m/s (D) 7.55 x 106 m/s