Practice Test for PBA Physics (Section A/Part I)

Question 1: In a slide wire bridge, the null point is obtained when:?

A) The galvanometer shows maximum deflection

B) The potential difference across the bridge is zero

C) The galvanometer shows zero deflection

D) The resistance of the wire is maximum

Explanation: At the null point, the galvanometer shows zero deflection, indicating a balanced bridge where the ratio of resistances is equal.

Question 2: The slide wire bridge operates on the principle of:

A) Ohm's Law

B) Wheatstone Bridge

C) Kirchhoff's First Law

D) Joule's Law

Explanation: The slide wire bridge is based on the Wheatstone Bridge principle, which allows for the determination of unknown resistance by balancing two legs of a bridge circuit.

Question 3: For accurate measurement using a slide wire bridge, the wire should:?

A) Have varying cross-sectional area

B) Be non-uniform

C) Have uniform cross-sectional area and material

D) Be made of insulating material

Explanation: A uniform wire ensures consistent resistance per unit length, which is essential for accurate measurements.

Question 4: If the balancing length is 60 cm and the known resistance is 10 Ω, the unknown resistance is:

A) 6 Ω

B) 10 Ω

C) 15 Ω

D) 20 Ω

Explanation: Using the formula R1/R2=L1/L2, where L1 is 60cm and L2 is 40cm then R2 is 10*40/60=6.67Ω (approximately 6Ω).

Question 5: The sensitivity of a slide wire bridge increases when:

A) The wire is shorter

B) The wire has higher resistance per unit length

C) A higher current is used

D) The galvanometer has low sensitivity

Explanation: Higher resistance per unit length increases the potential difference per unit length, enhancing sensitivity.

Question 6: To measure internal resistance using a potentiometer, the cell is connected:

A) Directly to the galvanometer

B) In parallel with the potentiometer wire

C) Without any resistance

D) Through a known external resistance

Explanation: A known external resistance is connected to the cell to create a potential drop, which is measured to determine internal resistance.

Question 7: A potentiometer is preferred over a voltmeter for measuring emf because:

A) It is less expensive

B) It provides more accurate measurements

C) It draws significant current

D) It is easier to use

Explanation: A potentiometer measures emf without drawing current from the cell, providing more accurate readings.

Question 8: Unit of distance

A) The length of the wire changes

B) The temperature changes

C) The external resistance changes

D) The internal resistance of the cell changes

Explanation: Changing the external resistance alters the current, affecting the potential drop and shifting the balance point.

Question 9: If the balance length without external resistance is 50 cm and with resistance is 40 cm, the internal resistance is:

A) Equal to external resistance

B) Less than external resistance

C) Greater than external resistance

D) Cannot be determined

Explanation: A shorter balance length with external resistance indicates a voltage drop, suggesting internal resistance is less than the external resistance.

Question 10: The emf of a cell is measured using a potentiometer by:

A) Connecting it directly to a voltmeter

B) Measuring the current through it

C) Finding the balance length

D) Calculating power output

Explanation: The balance length on the potentiometer wire corresponds to the emf of the cell when no current is drawn.

Question 11: A longer balance length on the potentiometer indicates::

A) Lower emf

Higher emf) J

C) Higher internal resistance

D) Lower internal resistance

Explanation: A longer balance length corresponds to a higher potential difference, indicating higher emf..

Question 12: The potentiometer wire must be:

A) Non-conductive

B) Uniform in resistance

C) Very short

D) Highly resistive

Explanation: Uniform resistance ensures accurate measurement of potential differences along the wire.

Question 13: The standard cell in a potentiometer setup is used to:

A) Power the circuit

B) Calibrate the potentiometer

C) Measure current

D) Increase sensitivity

Explanation: A standard cell with known emf is used to calibrate the potentiometer scale.

Question 14: In a V vs. I graph for a cell, the y-intercept represents:

A) Internal resistance

B) EMF

C) Terminal voltage

D) Current

Explanation: The y-intercept is the emf of the cell when current is zero.

Question 15: The slope of the V vs. I graph indicates:

A) EMF

B) Internal resistance

C) Power

D) Conductance

Explanation: The negative slope of the V-I graph represents the internal resistance of the cell.

Question 16: A straight-line V-I graph suggests:

A) Constant internal resistance

B) Variable emf

C) Non-ohmic behavior

D) Fluctuating current

Explanation: A straight line indicates a constant internal resistance and linear relationship between V and I.

Question 17: If the V-I graph has a slope of -2 Ω, the internal resistance is::

A) 2 Ω

B) -2 Ω

C) 0.5 Ω

D) Cannot be determined

Explanation: The magnitude of the slope gives the internal resistance; negative sign indicates voltage drop.

Question 18: Unit of current:

A) Decreasing emf

B) Increasing internal resistance

C) Voltage drop across internal resistance

D) Power loss

Explanation: As current increases, the voltage drop across internal resistance increases, reducing terminal voltage.

Question 19: The slope of the R vs. I/L graph gives:

A) Voltmeter resistance

B) Conductance

C) Internal resistance of the cell

D) Capacitance

Explanation: The slope directly corresponds to the resistance of the voltmeter.

Question 20: A high resistance voltmeter is preferred because:

A) It draws more current

B) It causes significant voltage drop

C) It minimizes current draw

D) It is cheaper

Explanation: High resistance ensures minimal current draw, reducing the impact on the circuit being measured.

Question 21: If the slope of the graph is 10, the voltmeter resistance is:

A) 0.1 Ω

B) 10 Ω

C) 100 Ω

D) Cannot be determined

Explanation: The slope value directly gives the voltmeter resistance in ohms.

Question 22: In an AC circuit with capacitors connected in parallel, the total capacitance is:

A) Less than smallest capacitor

B) Product of capacitances

C) Sum of reciprocals

D) Sum of individual capacitances

Explanation: In parallel combinations, capacitances simply add: Ceq=C1+C2+…

Question 23: As the total capacitance in an AC circuit increases, the capacitive reactance:

A) Increases

B) Decreases

C) Remains constant

D) Becomes infinite

Explanation: Capacitive reactance Xc=12πf, hence increasing C decreases Xc

Question 24: In an AC circuit, increasing the capacitance results in:

A) Increase in current

B) Decrease in current

C) No change in current

D) Zero current

Explanation: Higher capacitance reduces Xc, allowing more current to flow through the circuit.

Question 25: If three capacitors of 2 µF, 3 µF, and 5 µF are connected in parallel, the total capacitance is:

A) 10 µF

B) 0.625 µF

C) 1.25 µF

D) 5 µF

Explanation: Total parallel capacitance: Ctotal=2+3+5=10 µF.

Report Card

Total Questions Attempted: 0

Correct Answers: 0

Wrong Answers: 0

--