Physics-1997-Set I

Q1) Horizontal component of Earth’s magnetic field at a place is 3 times the vertical component. What is the value of angle of dip at this place? (Marks 1)
Ans1) tan = BV/BH = 1/3
or = 30o

Q2) Force between two point electric charges kept at a distance d apart in air is F. If these charges are kept at the same distance in water, how does the force between them change? (Marks 1)
Ans2) F = (1/4or) q1q2/r2
where r is the relative permittivity.
r = 1 for air & 81 for water.
Fa/Fw = 81/1
or Fw = 81 Fa

Q3) Give any two factors on which thermo-electric emf produced in a thermo-couple depends. (Marks 1)
Ans3) Thermoemf depends on
(i) Temp difference between the junctions
(ii) Nature of metals forming thermocouple

Q4) The electric current in a wire in the direction from B to A is decreasing. What is the direction of induced current in the metallic loop kept above the wire as shown in the figure? (Marks 1)

Induced current will be clockwise

Q5) Name the electromagnetic radiations used for viewing objects through haze and fog. (Marks 1)
Ans5) Infrared rays.

Q6) Give the ratio of the number of holes and the number of conduction electrons in an intrinsic semiconductor. (Marks 1)
Ans6) One

Q7) In the given diagram, is the diode D forward or reversed biased? (Marks 1)
Ans7) The diode is reverse biased since n-type is at a potential higher than p-type.

Q8) Name the planet which has maximum value of albedo.
(Marks 1)
Ans8) Venus

Q9) Two point electric charges of unknown magnitude and sign are placed a distance ‘d’ apart. The electric field intensity is zero at a point, not between the charges but on the line joining them. Write two essential conditions for this to happen. (Marks 2)
Ans9) (i) They should be of opposite signs
(ii) They must be of unequal magnitude.

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