Advertisements
Advertisements
प्रश्न
Electric field intensity in free space at a distance ‘r’ outside the charged conducting sphere of radius ‘R’ in terms of surface charge density ‘ a ’ is............................
(a)`sigma / in_0[R/r]^2`
(b)`in_0/sigma[R/r]^2`
(c)`R/r[sigma/in_0]^2`
(d)`R/sigma[r/in_0]^2`
Advertisements
उत्तर
(a) `sigma / in_0[R/r]^2`
Electric field intensity in the free space outside the charged conducting sphere in terms of surface charged density is given as
`E=sigma / in_0[R/r]^2`
APPEARS IN
संबंधित प्रश्न
The magnetic flux through a loop varies according to the relation Φ = 8t2 + 6t + C, where ‘C’ is constant, 'Φ' is in milliweber and 't' is in second. What is the magnitude of induced e.m.f. in the loop at t = 2 seconds.
State Fleming’s right-hand rule.
State three differences between direct current and alternating current.
A metal rod `1/sqrtpi `m long rotates about one of its ends perpendicular to a plane whose magnetic induction is 4 x 10-3 T. Calculate the number of revolutions made by the rod per second if the e.m.f. induced between the ends of the rod is 16 mV.
The phenomenon of electromagnetic induction is
Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
If ‘R’ is the radius of dees and ‘B’ be the magnetic field of induction in which positive charges (q) of mass (m) escape from the cyclotron, then its maximum speed (vmax) is _______.
A) `(qR)/(Bm)`
B)`(qm)/(Br)`
C) `(qBR)/m`
D) `m/(qBR)`
A circular coil of cross-sectional area 200 cm2 and 20 turns is rotated about the vertical diameter with angular speed of 50 rad s−1 in a uniform magnetic field of magnitude 3.0 × 10−2T. Calculate the maximum value of the current in the coil.
An emf of 2V is induced in a coil when the current in it is changed from 0A to 10A in 0·40 sec. Find the coefficient of self-inductance of the coil.
State three ways in which the strength of an electromagnet can be increased.
How does an electromagnet differ forma permanent magnet?
Name two devices in which electromagnets are used and two devices where permanent magnets are used.
Explain why, an electromagnet is called a temporary magnet.
State the factors on which the strength of an electromagnet depends. How does it depend on these factors?
Write some of the important uses of electromagnets.
The direction of current in the coil at one end of an electromagnet is clockwise. This end of the electromagnet will be:
(a) north pole
(b) east pole
(c) south pole
(d) west pole
When current is 'switched on' and 'switched off' in a coil, a current is induced in another coil kept near it. What is this phenomenon known as?
When the magnet shown in the diagram below is moving towards the coil, the galvanometer gives a reading to the right.
() What is the name of the effect being produced by the moving magnet?
(2) State what happens to the reading shown on the galvanometer when the magnet is moving away from the coil.
(3) The original experiment is repeated. This time the magnet is moved towards the coil at a great speed. State two changes you would notice in the reading on the galvanometer.
How is the working of an electric bell affected, if alternating current be used instead of direct current?
Show diagrammatically how an alternating emf is generated by a loop of wire rotating in a magnetic field. Write the expression for the instantaneous value of the emf induced in the rotating loop.
Electromagnetic induction means ______.
The coil of a moving-coil galvanometer keeps on oscillating for a long time if it is deflected and released. If the ends of the coil are connected together, the oscillation stops at once. Explain.
L, C and R represent the physical quantities inductance, capacitance and resistance respectively. Which of the following combinations have dimensions of frequency?
(a) `1/(RC)`
(b) `R/L`
(c) `1/sqrt(LC)`
(d) C/L
A conducting square loop having edges of length 2.0 cm is rotated through 180° about a diagonal in 0.20 s. A magnetic field B exists in the region which is perpendicular to the loop in its initial position. If the average induced emf during the rotation is 20 mV, find the magnitude of the magnetic field.
Draw and label the diagram of a simple D.C. motor.
(a) Explain the rotation of the coil, giving a reason for your answer.
(b) How can you reverse the direction of rotation of the armature?
(c) How can you increase the speed of rotation of the motor?
Fill in the blanks by writing (i) Only soft iron, (ii) Only steel, (iii) Both soft-iron and steel for the material of core and/or magnet.
D.C. motor ______.
Name the following diagram and explain the concept behind it.

What is an electromagnet? What do you know about the simplest form of an electromagnet?
The diagram shows a rectangular coil ABCD, suspended freely between the concave pole pieces of a permanent horseshoe magnet, such that the plane of the coil is parallel to the magnetic field.

- State your observation when the current is switched on.
- Give an explanation for your observation in (i).
- State the rule, which will help you to find the motion of rotation of the coil.
- In which position will the coil ultimately come to rest?
- State four ways of increasing the magnitude of force acting on the coil.
The energy stored in a 50 mH inductor carrying a current of 4 A is ______
State the condition at which we say the two coils kept close to each other are perfectly coupled with each other.
Observe the given figure of Fleming’s Right Hand Rule and write the labels of A and B correctly.

Find the odd one out and give its explanation.
Write Fleming’s right hand thumb rule with the help of diagram.
An electron moves on a straight-line path XY as shown in the figure. The coil abcd is adjacent to the path of the electron. What will be the direction of the current, if any, induced in the coil?

A thin semi-circular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure.

The potential difference developed across the ring when its speed v , is
Give an illustration of determining direction of induced current by using Lenz’s law.
Obtain an expression for motional emf from Lorentz force.
A square coil of side 30 cm with 500 turns is kept in a uniform magnetic field of 0.4 T. The plane of the coil is inclined at an angle of 30° to the field. Calculate the magnetic flux through the coil.
A 50 cm long solenoid has 400 turns per cm. The diameter of the solenoid is 0.04 m. Find the magnetic flux linked with each turn when it carries a current of 1 A.
A cylindrical bar magnet (A) and similar unmagnetized cylindrical iron bar (B) are dropped through metallic pipe. The time taken to come down by ____________.
A metal plate can be heated by ______.
Name some equipment that uses electromagnetism for functioning.
For making a strong electromagnet the material of the core should be ______.
A 0.4 m wire, stretched horizontally, carries an electric current of 15 A, in a magnetic field whose magnetic field intensity is 0.1 N/Am. What is the magnitude of the wire?
A conductor of length 50 cm carrying a current of 5 A is placed perpendicular to a magnetic field of induction 2×10 -3T. Find the force on the conductor.
The working of a dynamo is based on the principle of
Show that for a given positive ion species in a cyclotron, (i) the radius of their circular path inside a dee is directly proportional to their speed, and (ii) the maximum ion energy achievable is directly proportional to the square of the magnetic induction.
When an electric current is passed through a wire or a coil, a magnetic field is produced. Is the reverse phenomenon possible i.e, can a magnetic field produce an electric current? Explain with the help of an appropriate example.
