Fluorescent Lamp Power Consumption

• The experiment aims to connect and measure the power consumption of a fluorescent lamp.

Apparatus Required

• Ammeter (MI TYPE): 0.5/1A, Quantity: 1
• Voltmeter (MI TYPE): 0-300V, Quantity: 1
• Wattmeter: 0.5/1A,300V, Quantity: 1
• Autotransformer: 0-270V,10A, Quantity: 1
• Fluorescent lamp: 40W, Quantity: 1
• Starter: Glow type, Quantity: 1
• Choke: 40W,230V, Quantity: 1
• Connecting wire: As per required

Theory

• The starter electrode inside an argon-filled gas bulb initiates a discharge in the argon gas, generating heat.
• Upon heating, a bimetallic strip bends, closing the starter circuit, connecting the choke and tube filaments in series.
• Current flowing through the filaments produces heat, causing the starter tube discharge to cease and the starter contacts to separate.
• The separation of starter terminals results in a sudden circuit break, inducing a high electromotive force (e.m.f) in the choke.
• According to Lenz's law, the induced e.m.f in the choke opposes the current decrease.
• The sufficient voltage across the tube ends triggers a discharge in the gas inside the tube, initiating light emission.
• The fluorescent lamp contains a small amount of mercury and argon gas at 2.5 mm pressure inside a long evacuated tube.
• Filled with argon gas to start the tube mercury is initially in small drops.
• Argon gas initially burns at the tube ends, heating the mercury until the tube starts emitting light.
• A tungsten electrode coated with fast electron-emitting material is at each end of the tube.
• The interior tube surface is coated with phosphor light.
• The starter helps start the tube and break the circuit.
• The choke coil, also called a ballast, features a laminated core with enameled wire.
• The function of the choke coil is to initially increase the voltage to approximately 1000V when switching on the tube.
• The choke reduces the voltage across the tube.

Procedure

• Connect the circuit as per the circuit diagram.

• Ensure the autotransformer is at its minimum or zero voltage position before switching on the power supply.

• Gradually increase the autotransformer's output voltage until the tube light glows ("PICK UP VOLTAGE"), recording the voltmeter, ammeter, and wattmeter readings.

• Increase the voltage to the tube light's rated voltage and record the readings from all meters.

• Gradually decrease the voltage, watching for the tube light to flicker ("CUT OFF VOLTAGE") before going out.

• After confirming the output voltage is at zero, switch off the power.

• Resistance of a winding is defined by Ohm's Law as ratio of voltage applied across the winding, to the current flowing through it (R=V/I).

• The armature generates emf in a generator and torque in a motor. Carries higher currents, so designed for low resistance to minimize voltage drop.

• Shunt field winding in parallel with armature.

• Field current is less than armature current, thus the shunt winding has a high resistance.

• Vary the DC supply and set the ammeter reading, then record the voltmeter reading.

• Reduce the output voltage of DC supply to minimum position, and then switch OFF.

• In a series R-L-C circuit, the current is the same through all elements.

• The resultant applied voltage is the phasor sum of the voltages across each element.

• Voltage across the resistance (VR) equals IR.

• Voltage across the inductance (VL) equals IXL.

• Voltage across the capacitance (VC) equals IXC.

• Voltage applied across the circuit (V) equals IZ.

• Power drawn by the circuit (P) equals VI cosφ.

• Power factor of the circuit is P/VI.

• Inductive reactance (XL) equals ωL or 2πfL.

• Capacitive reactance (XC) equals 1/ωC or 1/2πfL.

• Impedance (Z) of the circuit is √[R² + (ωL - 1/ωC)²].

• Current (I) flowing in the circuit is V / √[R² + (ωL - 1/ωC)²].

• Power factor (cosφ) is R / √[R² + (ωL - 1/ωC)²].

• The power factor is lagging if ωL > 1/ωC, and leading if ωL < 1/ωC.