9 Most VSAQ’s of Alternating Current Chapter in Inter 2nd Year Physics (TS/AP)

2 Marks

VSAQ-1 : What type of transformer is used in a 6V bed lamp?

In a 6V bed lamp, a step-down transformer is used to reduce the higher household supply voltage (220V-240V AC) to the lower voltage required for the lamp, which is 6V AC. If the lamp operates on DC power, a rectifier would also be necessary to convert the 6V AC to 6V DC. The step-down transformer has a turn ratio of 6:240, enabling it to reduce the voltage from the higher household supply to the desired 6V for the lamp.

VSAQ-2 : What is the phenomenon involved in the working of a transformer?

The working of a transformer involves the phenomenon of electromagnetic induction, specifically mutual induction. When an alternating current (AC) flows through the primary coil (input coil) of the transformer, it generates a changing magnetic field around it. This changing magnetic field, in turn, induces a voltage in the secondary coil (output coil) through mutual induction, resulting in the generation of a secondary current. The transformer utilizes this process to either step up or step down the voltage from the primary to the secondary coil, depending on the respective number of turns in each coil.

VSAQ-3 : What is transformer ratio?

The transformer ratio, also referred to as the turns ratio, is a critical parameter of a transformer. It is defined as the ratio of the number of turns in the secondary coil to the number of turns in the primary coil. This turns ratio plays a fundamental role in determining how the transformer either steps up or steps down the voltage. For example, if the turns ratio is 1:2, the secondary voltage will be twice the primary voltage, and if it is 2:1, the secondary voltage will be half of the primary voltage.

VSAQ-4 : Write the expression for the reactance of (i) an Inductor and (ii) a Capacitor

The expressions for reactance in an AC circuit are:

  1. Reactance of an Inductor (XL​): $$X_L = 2\pi fL$$ Where XL​ is the inductive reactance, f is the frequency in hertz (Hz), and L is the inductance in henrys (H).
  2. Reactance of a Capacitor (XC​): $$X_C = \frac{1}{2\pi fC}$$​ Where XC​ is the capacitive reactance, f is the frequency in hertz (Hz), and C is the capacitance in farads (F).

VSAQ-5 : What is the phase difference between AC e.m.f and AC current in the following : Pure Resistor, Pure Inductor and Pure capacitor.

The phase differences between AC electromotive force (emf or voltage) and AC current in various components are as follows:

  1. Pure Resistor: The phase difference is zero degrees, indicating that voltage and current are in phase, reaching their maximum and minimum values simultaneously.
  2. Pure Inductor: The voltage leads the current by 90 degrees, meaning the voltage reaches its extrema before the current.
  3. Pure Capacitor: The current leads the voltage by 90 degrees, implying that the current reaches its extrema before the voltage.

VSAQ-6 : What is the phase difference between AC e.m.f and current in the following ? Pure resistor & Pure Inductor.

The phase difference between AC electromotive force (e.m.f or voltage) and current in the following components is as follows:

  1. Pure Resistor: In a pure resistor, the phase difference is zero degrees. This means that the voltage and current are in phase, reaching their maximum and minimum values at the same time.
  2. Pure Inductor: In a pure inductor, the voltage leads the current by 90 degrees. This indicates that the voltage reaches its maximum or minimum value before the current reaches its maximum or minimum value.

VSAQ-7 : A transformer converts 200 V ac into 2000 V ac. Calculate the number of turns in the secondary if the primary has 10 turns.

The number of turns in the secondary coil of the transformer, given a primary coil with 10 turns and a voltage transformation from 200 V AC to 2000 V AC, is 100 turns in the secondary coil.

VSAQ-8 : What is Step-up transformer ? How it differs from Step-down transformer?

A step-up transformer increases voltage from the primary to the secondary coil by having more turns in the secondary. It is used in power transmission.

Difference from a step-down transformer:

  1. Step-up increases voltage, while step-down reduces it.
  2. More turns in the secondary for step-up, and more turns in the primary for step-down.
  3. Step-up is used for transmission, while step-down is used for appliances and safety.

VSAQ-9 : What is meant by wattless component of current?

The wattless component of current refers to a type of current in a circuit that does not consume or deliver any real power (watts). It occurs when the circuit contains either only inductive components (like coils) or only capacitive components (like capacitors). This type of current is often referred to as “reactive current” and is associated with the exchange of energy between the electric and magnetic fields in the components, but without actually doing any useful work or dissipating power. It is called “wattless” because it does not contribute to real power consumption or generation in the circuit.