In a fluorescent tube light, what is the main purpose of the choke or ballast in the electrical circuit?

Introduction / Context:
Fluorescent tube lights, commonly called tube lights, use a gas discharge to produce light. The electrical circuit that drives a tube light includes a component called a choke or ballast. Understanding the role of this choke is a standard topic in basic electricity and household appliance physics. This question focuses on the main function of the choke during the starting of the tube light.

Given Data / Assumptions:

• The circuit of a typical fluorescent tube includes a choke (ballast), a starter and the tube itself.
• The tube contains low pressure gas and requires a high voltage to initiate discharge.
• Normal supply voltage is not always sufficient to start the discharge without assistance.
• The choke is an inductive component that can briefly generate higher voltages when current is interrupted.

Concept / Approach:
A fluorescent tube needs a higher voltage to strike an arc across its length than to keep that arc running once it has started. The choke or ballast is basically an inductor. When the starter opens the circuit after preheating the filaments, the rapid interruption of current through the inductor produces a momentary high induced voltage according to the law of electromagnetic induction. This increased voltage appears across the tube and helps to ionise the gas and start the discharge. After ignition, the choke also helps limit the current to a safe value, but the most commonly emphasised function in school level questions is to provide a high starting voltage.

Step-by-Step Solution:
Step 1: Recognise that gas discharge tubes require a higher voltage to start than to continue operating.Step 2: Identify the choke as an inductor placed in series with the tube.Step 3: When the starter opens, the current through the inductor is suddenly interrupted.Step 4: This sudden change in current produces a large voltage spike across the inductor due to electromagnetic induction.Step 5: This high induced voltage appears across the tube ends and helps ionise the gas and start the arc.Step 6: Once the tube is lit, the choke continues to limit current, but its primary textbook purpose is to provide high starting voltage.

Verification / Alternative check:
Practical descriptions of tube light circuits usually show the choke as a series inductor and explain that it generates an inductive kick when the starter opens, used to strike the tube. Modern electronic ballasts perform similar functions using solid state circuits, but the underlying need for a starting overvoltage remains. This supports the conclusion that inducing high voltage is the primary role of the choke in traditional tube lights.

Why Other Options Are Wrong:
Providing very low resistance is not the main purpose; in fact, without current limiting the tube would draw excessive current once started. Providing a very high constant resistance would waste power and is not how a choke functions, since inductors resist changes in current rather than acting as simple resistances. Inducing a low voltage would not help start the tube; it is the high voltage that is needed to ionise the gas and strike the discharge.

Common Pitfalls:
Some learners confuse the choke with a simple resistor and talk only about current limiting, forgetting the starting role. Others think of it as a transformer and assume it always steps down voltage. To avoid such misunderstandings, remember that a choke in a tube light acts as an inductor that produces a brief high voltage pulse when current is interrupted, making it easier to start the discharge in the tube.

Final Answer:
The main purpose of the choke in a tube light is to induce a high voltage across the tube at the time of starting.