When the fluorescent tube is switched on almost full supply voltage is applied to the starter. The potential across bimetallic electrodes of the starter causes a small glow discharge at a small current not enough to heat up the tube filaments. This discharge is enough to heat the bimetallic strips of the starter itself causing them to bend and make contact. As a result, the large current flows through the electrodes their temperature being raised to incandescence and the gas in the immediate neighborhood inside the tube gets ionized. At the same time when the contacts of the starter are closed potential difference across it is reduced to zero. After two or three seconds glow discharge inside the starter stops and the bimetallic strips cool down which breaks the contacts apart. This sudden break induces a very high voltage in the coke connected in series due to its inertia effect and it is sufficient to initiate the discharge in the main tube light. When the fluorescent tube is alight, current passes through the tube which offers a very low resistance. The voltage across the tube is about 110 volts and rest of the supply voltage of about 110 volts is dropped in the choke. Due to the low voltage, the starter ceases to glow. Starters are so designed that this potential difference across the lamp in running condition is insufficient to restart the glow discharge in the starter. So the contacts remain open, thus the tube is put in operation.
To suppress the radio interference a condenser of about 0.05 μF capacity is connected in parallel with the starter.
A resistance of about 100 ohms is connected in series with the radio suppressor condenser to check the condenser surges so as to prevent the starter contacts welding together.
To improve the power factor a condenser is connected across the supply line. The size of the condenser should be 3.25μF for 40 watt and 7.5 μF for 80 watt lamps.
Yes, the choke is necessary to create the voltage impulse at the time of starting.
As there is no effect of inductance on d.c. supply an extra variable resistance is connected in series with the choke to increase the effective resistance to absorb the difference between the mains voltage and the correct lamp voltage during running.
A reversing switch is used to reverse the current at intervals to prevent the blackening of the tube at positive end due to migration of the mercury from the positive end to the negative end of the tube.
Fluorescent tube light.
Fluorescent lamps are most commonly used due to its following advantages over other light sources :- (a)Increased efficiency, (b) Longer life of lamp, (c) Gives illumination in a variety of colours, (d) Gives glare or glitter free light, (e) High lighting intensities are achieved without excessive temperature rise, (f) Gives diffused and shadow light, (g) Gives more comfortable illumination and (h) Through initial cost is more it is economical.
The light efficiency in fluorescent tube light is high because the invisible radiation is converted into visible radiation with the action of phosphor coating inside the tube which reduces the loss light energy.
Multiple Choice Question (MCQ) of Electronics page-17:241. Which of the following statement is true? a) The saturation voltage VCF of silicon transistor is more than germanium transistor. b) The saturation voltage VCE for germanium transistor is more than silicon transistor. c) The saturation voltage VCE for silicon transistor is same as that for germanium. d) The saturation voltage VCE for silicon transistor is lower than germanium transistor.
Multiple Choice Question (MCQ) of Electronics page-16:226. Which of the following statement is correct? a) Inner electrons are always present in the semiconductor. b) Bound electrons are always present in the semiconductor. c) Free electrons are always present in the semiconductor. d) Inner and bound electrons are always present in the semiconductor.
Multiple Choice Question (MCQ) of Electronics page-15:211. The materials whose electrical conductivity is usually less than 1 × 106 mho/m are a) Semiconductors b) Conductors c) Insulators d) Alloys
Multiple Choice Question (MCQ) of Electronics page-14:196. In which of the following device the base resistors are not added in the package but added externally? a) UJT b) CUJT c) PUT d) None of the above
Multiple Choice Question (MCQ) of Electronics page-13:181. The conduction in JEFT is always by the a) Majority carriers b) Minority carriers c) Holes d) Electrons e) Holes and electrons simultaneously