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A photocell is a technological application of the photoelectric effect. It is a device whose electrical properties are affected by light. It is also sometimes called an electric eye. Photocells are used in the reproduction of sound in motion pictures and in the television camera for scanning and telecasting scenes. They are used in industries for detecting minor flaws or holes in metal sheets.
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An electric field is a field or space around an electrically charged object where any other electrically charged object will experience a force. An electric field is measured by a term known as electric field intensity. In that case, line through which the positive unit charge moves, is called line of force.
Electric field, an electric property associated with each point in space when charge is present in any form. ... The magnitude and direction of the electric field are expressed by the value of E, called electric field strength or electric field intensity or simply the electric field.
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Wavefront
- Wave front is defined as locus of all points having same phase at a given instant of time.
- The shape of wavefront depends on the shape of the source of disturbance.
- A wavefront is always normal to the light rays.
- A wavefront does not propagate in the backward direction.
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Galvanometer is an electromechanical instrument which is used for the detection of electric currents through electric circuits. Being a sensitive instrument, Galvanometer can not be used for the measurement of heavy currents. However we can measure very small currents by using galvanometer but the primary purpose of galvanometer is the detection of electric current not the measurement of current.
Galvanometer works on the principle of conversion of electrical energy into mechanical energy. When a current flows in a magnetic field it experiences a magnetic torque. If it is free to rotate under a controlling torque, it rotates through an angle proportional to the current flowing through it.
here are five essential parts of a Galvanometer.
1. A U-shaped permanent magnet with concave poles.
2. Flat rectangular coil of thin enameled insulated wire ‘C’.
3. A soft iron cylinder 'B'.
4. A pointer or needle.
5. A scale.
The flat rectangular coil of thin enameled insulated wire of suitable number of turns wound on a light nonmetallic or aluminum frame is suspended between the cylindrically concave poles of magnet by a thin phosphor bronze strip. One end of the wire of the coil is soldered to strip. The other end of the strip fixed to the frame of the galvanometer and connected to an external terminal. It serves as one leas current lead through which the current enters or leaves the coil. The other end of the wire of the coil is soldered to a loose and soft spiral of wire connected to another external terminal. The soft spiral of a wire serves as the other current lead. A soft-iron cylinder, coaxial with the pole pieces, is placed within the frame of the coil and is fixed to the body of the galvanometer. In the space between it and the pole pieces, where the coil moves freely, the soft iron cylinder makes the magnetic field stronger and radial such that into whatever position the coil rotates, the magnetic field is always parallel to its plane.
When a current passes through the galvanometer coil, it experiences a magnetic deflecting torque, which tends to rotate it from its rest position. As the coil rotates it produces a twist in the suspension strip. The twist in the strip produces an electric restoring torque. The coil rotates until the elastic restoring torque due to the strip does not equal and cancels the deflecting magnetic torque, then it attains equilibrium and stops rotating any furthers.
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A collision occurs when two objects come in direct contact with each other. It is the event in which two or more bodies exert forces on each other in about a relatively short time.
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Electric flux is the rate of flow of the electric field through a given area (see ). Electric flux is proportional to the number of electric field lines going through a virtual surface.
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate force in the form of torque applied on the motor's shaft.
Posted by Shruti Sharma 5 years, 1 month ago
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MOVING COIL GALVANOMETER:
- Moving coil galvanometer is an electromagnetic device that can measure small values of current. It is also known as Weston galvanometer.
- It works on the principle that when a current loop is placed in an external magnetic field, it experiences torque, and the value of torque can be changed by changing the current in the loop
- Moving coil galvanometer consists of permanent horse-shoe magnets, coil, soft iron core, pivoted spring, non-metallic frame, scale and pointer
- We know that a current loop having N number of turns,and the cross sectional area A, carrying current i, when placed in and along the direction of external magnetic field B, experiences a torque given by:
ԏ = NiAB
The pivoted spring of spring constant k would oppose the above torque with restoring torque C given by: C = kΦ
Here, Φ is the angular deflection of spring
- Both, the torque, and the restoring torque would be equal:
kΦ = NiAB
Φ = NiAB/k
- In the above equation, except for current, every other quantity on the right hand side is constant for a galvanometer, hence:
Φ ∝ i
- So, the angular deflection Φ produced in the pointer could be measured in terms of current in the scale calibrated on the basis of above equations.
- To use galvanometer as an ammeter (to measure higher values of current), we need to connect a shunt wire, with very small resistance(Rs), in parallel with the galvanometer (which have very low resistance of Rg
Equivalent resistance R of ammeter will be:
R = RgRs/(Rg + Rs)
Rg ˃˃ Rs
∴ R = RgRs/Rg = Rs
- So, the equivalent resistance of ammeter is very less, which is a must for sensitivity of ammeter to be higher. Also, most of the current will pass through the shunt, thus protecting the galvanometer from any damage.
- Ammeter is connected in series with the circuit where current is to be measured
- Current sensitivity(deflection per unit current) of galvanometer is given by:
Φ/i = NAB/k
- To use galvanometer as a voltmeter, we need to connect a wire, with very high resistance(Rw˃˃Rg), in series with the galvanometer to ensure that our voltmeter equivalent resistance is high and so that it will draw a very small current. Equivalent resistance will be given by:
R = Rg + Rw = Rw
Voltmeter is connected in parallel with the circuit where voltage is to be measured
- Voltage sensitivity (deflection per unit voltage) of galvanometer is given by:
Φ/V = NAB/(kR)
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