Circuit Theory (ECE) test-1

The total resistance in a parallel combination of resistors R1​ and R2​ is given by:

• R _total =R₁+ R₂

• R _total =R₁ R₂

Answer explanation

In a parallel combination, the total resistance is calculated using the formula R_total = (R1 * R2) / (R1 + R2). This reflects how the resistors share the current, making the correct choice the second option.

The total power in an AC circuit with a resistor is:

• Active power

• Reactive power

• Apparent power

• None of the above

Answer explanation

In an AC circuit with a resistor, the total power is referred to as active power. This is the power that performs work in the circuit, unlike reactive power, which does not contribute to work.

For a series R-L circuit, the phase angle between the current and the voltage is:

• 0 degrees

• 45 degrees

• 90 degrees

• Depends on R and L values

Answer explanation

In a series R-L circuit, the phase angle between current and voltage depends on the values of resistance (R) and inductance (L). It is given by the formula tan(φ) = X_L/R, where X_L is the inductive reactance.

Kirchhoff’s Voltage Law (KVL) is based on the principle of:

• Conservation of charge

• Conservation of energy

• Conservation of current

• Conservation of power

Answer explanation

Kirchhoff’s Voltage Law (KVL) states that the sum of the electrical potential differences (voltages) around any closed circuit is zero, reflecting the conservation of energy in electrical systems.

For an R-C series circuit, the phase angle between the current and the voltage is:

• 0 degrees

• 45 degrees

• 90 degrees

• Between 0 and 90 degrees

Answer explanation

In an R-C series circuit, the phase angle between the current and voltage is determined by the reactance of the capacitor and the resistance. It is always between 0 and 90 degrees, indicating that the current lags the voltage.

The unit of capacitance is:

• Farad

• Henry

• Ohm

• Tesla

Answer explanation

The unit of capacitance is the Farad, which measures a capacitor's ability to store charge. Henry measures inductance, Ohm measures resistance, and Tesla measures magnetic flux density.

What is the unit of bandwidth?

• Hertz

• Seconds

• Decibels

• Ohms

Answer explanation

The unit of bandwidth is measured in Hertz (Hz), which represents cycles per second. It indicates the range of frequencies a system can transmit or receive, making Hertz the correct choice.

If a signal occupies a frequency range from 1 MHz to 5 MHz, what is its bandwidth?

• 4 MHz

• 5 MHz

• 1 MHz

• 6 MHz

Answer explanation

The bandwidth of a signal is calculated by subtracting the lower frequency from the upper frequency. Here, 5 MHz - 1 MHz = 4 MHz, making the correct answer 4 MHz.

Which factor does NOT affect the bandwidth of a transmission medium?

• Material of the medium

• Length of the medium

• Modulation technique

• Gravitational force

Answer explanation

Gravitational force does not influence the bandwidth of a transmission medium. In contrast, the material, length, and modulation technique directly impact how data is transmitted and the medium's capacity.

What is the typical bandwidth of a voice channel in telephony?

• 300 Hz to 3.4 kHz

• 20 Hz to 20 kHz

• 1 kHz to 10 kHz

• 0 Hz to 300 Hz

Answer explanation

The typical bandwidth of a voice channel in telephony is 300 Hz to 3.4 kHz. This range effectively captures the frequencies necessary for clear voice communication, making it the correct choice.