51.

A circuit has a resistance of 12 Ω and an impedance of 15 Ω. The power factor of the circuit will be

• 0.8

• 0.4

• 1.25

• 1.25

The phase difference between the alternating current and emf is π/2. Which of the following cannot be the constituent of the circuit?

• C alone

• R.L

• L.C

• L.C

A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected along the direction of the fields with a certain velocity then

• its velocity will decrease.

• its velocity will increase.

• it will turn towards right of direction of motion.

• it will turn towards right of direction of motion.

A charged particle of mass m and charge q travels on a circular path of radius r that is perpendicular to a magnetic field B. The time taken by the particle to complete one revolution is

In a potentiometer experiment, the balancing with a cell is at length 240 cm. On shunting, the cell with a resistance of 2Ω the balancing length becomes 120 cm. The internal resistance of the cell is

• 1 Ω

• 0.5 Ω
  

• 3 Ω

• 3 Ω

The resistance of hot tungsten filament is about 10 times the cold resistance. What will be the resistance of 100 W and 200 V lamp when not in use?

• 40 Ω

• 20 Ω

• 400 Ω

• 400 Ω

A magnetic needle is kept in a non-uniform magnetic field. It experiences

• a torque but not a force

• neither a force nor a torque

• a force and a torque.

• a force and a torque.

• 1.8 pF

• 40.5 pF

• 45 pF
• 45 pF

• 6 x 10^-7 C/m²
• 3  x 10^-7 C/m²
• 3 x 10⁴ C/m²
• 3 x 10⁴ C/m²

Two sources of equal emf are connected to an external resistance R. The internal resistances of the two sources are R₁ and R₂ (R₂>R₁). If the potential difference across the source having internal resistance R₂ is zero, then

• 

• R = R₂-R₁

• 
•