The potential energy of a molecule on the surface of a liquid compared to one inside the liquid is
zero
lesser
equal
greater
Two spherical conductors B and C having equal radii and carrying equal charges in them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that of B but uncharged, is brought in contact with B, then brought in contact with C and finally removed away from both. The new force of repulsion between B and C is
In gamma ray emission from a nucleus
both the neutron number and the proton number change
there is no change in the proton number and the neutron number
only the neutron number changes
only the proton number changes
The resistance of an ammeter is 13 Ω and its scale is graduated for a current upto 100 A. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 A by this meter. The value of
shunt resistance is
20 Ω
2 Ω
0.2 Ω
2 KΩ
The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux linked with the primary coil is given by where is weber, t is time in second and is a constant, the output vltage across the secondary coil is
90 v
120 V
220 V
30 V
A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately
30%
50%
90%
10%
A charged particle (charge q) is moving in a circle of radius R with uniform speed v. The associated magnetic moments given by
qνR2
qνR
A steady current of 1.5 A flows through a copper voltameter for 10 min. If the electrochemical equivalent of copper is 30x 10-5 g C-1 , the mass of copper deposited on the electrode will be
0.40 g
0.50 g
0.67 g
0.27 g
D.
0.27 g
If m is the mass of a substance deposited or liberated at an electrode during electrolysis when a charge q passes through electrolyte, then according to Faraday's first law of electrolysis,
m ∝ q
⇒ m = zq
where z is a constant of proportionality and is called electrochemical equivalent (ECE) of the substance.
If an electric current I flows through the electrolyte, then
q = (I.t)
m = zIt
Here , I = 1.5 A,
t = 10 min = 10 × 60 s
z = 30 × 10-5 gC-1
Hence, mass of copper deposited on the electrode
m = 30 × 10-5 × 1.5 × 10 × 60
= 27 × 10-2
m = 0.27 g
In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular paths of radius R using a magnetic field B. If V and B are kept constant the ratio will be proportional to
R2
R
Three resistances P, Q, R each of 2Ω and an unknown resistance S form the four arms of a Wheatstone's bridge circuit. When a resistance of 6Ω is connected in parallel to S the bridge gets balanced. What is the value of S?
2 Ω
3 Ω
6 Ω
1 Ω