HSC Science (Electronics) 12th Standard Board Exam - Maharashtra State Board Question Bank Solutions

The string of a guitar is 80 cm long and has a fundamental frequency of 112 Hz. If a guitarist wishes to produce a frequency of 160 Hz, where should the person press the string?

Currents of equal magnitude pass through two long parallel wires having a separation of 1.35 cm. If the force per unit length on each of the wires is 4.76 x 10^-2 N, what must be I ?

Two wires shown in the figure are connected in a series circuit and the same current of 10 A passes through both, but in opposite directions. The separation between the two wires is 8 mm. The length AB is 22 cm. Obtain the direction and magnitude of the magnetic field due to current in wire 2 on the following figure segment AB of wire 1. Also, obtain the magnitude and direction of the force on wire 1. [μ₀ = 4π × 10^-7 T.m/A]

Two long parallel wires, both carrying current I directed into the plane of the page, are separated by a distance R. Show that at a point P equidistant from the wires and subtending an angle θ from the plane containing the wires, the magnitude of the magnetic field is B = `(mu_0)/pi "I"/"R"` sin 2θ. What is the direction of the magnetic field?

A very long straight wire carries a current of 5.2 A. What is the magnitude of the magnetic field at a distance 3.1 cm from the wire?

The magnetic field at a distance of 2.4 cm from a long straight [current-carrying] wire is 16 µT. What is the current through the wire?

The figure shows a cylindrical wire of diameter a, carrying a current I. The current density in the wire is in the direction of the axis and varies linearly with radial distance r from the axis according to the relation J = `"J"_0 "r"/"a"`. Obtain a magnetic field B inside the wire at a distance r from its center.

In the problem, what will be the magnetic field B inside the wire at a distance r from its center, if the current density J is uniform across the cross-section of the wire? Figure shows a section of a very long cylindrical wire of diameter a, carrying a current I. The current density which is in the direction of the central axis of the wire varies linearly with radial distance r from the axis according to the relation J = J_o r/a.

A long solenoid has turns per unit length 1.5 x 10³ per meter and area of cross-section 25 cm². A coil C of 150 turns is wound tightly around the center of the solenoid. For a current of 3 A in the solenoid, calculate
(a) the magnetic flux density at the centre of the solenoid
(b) the flux linkage in the coil C
(c) the average emf induced in coil C if the current in the solenoid is reversed in the direction in a time of 0.5 s. [µ₀ = 4π x 10^-7 H/m]

Insect moves over the surface of water because of ______.

The water droplets are spherical in free fall due to ______ 

The surface tension of a liquid at critical temperature is ______ 

Define surface tension.

What will be the shape of the liquid meniscus for the obtuse angle of contact? 

Water rises to a height of 20 mm in a capillary tube. If the radius made 1/3^rd of its previous value, to what height will the water now rise in the tube?  

Two soap bubbles have a radius in the ratio of 2:3. Compare the works done in blowing these bubbles.  

Explain the phenomena of surface tension on the basis of molecular theory.

Obtain an expression for the capillary rise or fall using the forces method.  

A u-tube is made up of capillaries of bore 1 mm and 2 mm respectively. The tube is held vertically and partially filled with a liquid of surface tension 49 dyne/cm and zero angles of contact. Calculate the density of the liquid, if the difference in the levels of the meniscus is 1.25 cm. take g = 980 cm/s²  

In a second’s pendulum, the mass of Bob is 50 g. If it is replaced by 100 g mass, then its period will be ______.