A transformer takes 2.0 A from a 230 V supply and delivers 9.0 A at 46 V. What is its efficiency?
Correct answer A. 90%
Subject / 480 questions
MDCAT ECAT Physics MCQs
Page 9 of MDCAT ECAT Physics multiple-choice questions with answers. Tap an option to check yourself.
Page 9 of 24
- Electromagnetic Induction 30
- Fluid Dynamics 30
- Electrostatics 30
- Electronics 30
- Electromagnetism 30
- Current Electricity 30
- Work and Energy 30
- Waves 30
- Vectors and Equilibrium 30
- Nuclear Physics 30
- Dawn of Modern Physics 30
- Thermodynamics 30
- Rotational and Circular Motion 30
- Atomic Spectra 30
- Alternating Current 30
- Force and Motion 30
Which statement about a step-up transformer is correct?
Correct answer C. The secondary has more turns and carries a smaller current than the primary
Why is electrical power transmitted over long distances at very high voltage?
Correct answer C. The current is reduced, so I²R losses in the cables are reduced
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A power station sends 100 kW through cables of total resistance 5.0 Ω. What power is lost as heat in the cables if transmission is at 10 kV?
Correct answer D. 500 W
If the transmission voltage for a fixed power is increased by a factor of 10, by what factor is the power lost in the transmission lines reduced?
Correct answer D. 100
In the national grid, what type of transformer is used near homes and factories?
Correct answer A. Step-down transformer
In a transformer, what are copper losses and how are they reduced?
Correct answer C. Heating in the windings due to their resistance, reduced by using thick copper wire
A bar magnet is held stationary inside a coil connected to a galvanometer. What does the galvanometer show?
Correct answer D. Zero reading
A coil of resistance 5.0 Ω has its flux linkage changed uniformly by 0.60 Wb-turns in 0.30 s. What current is induced in it?
Correct answer A. 0.40 A
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A coil of 50 turns and area 0.020 m² lies perpendicular to a magnetic field which rises uniformly from 0 to 0.80 T in 0.20 s. What is the induced emf?
Correct answer B. 4.0 V
What does the negative sign in Faraday’s law, ε = −NΔΦ/Δt, indicate?
Correct answer B. The induced emf opposes the change in flux that produces it
A straight metal rod moves through a uniform magnetic field with its velocity parallel to the field lines. What emf is induced in the rod?
Correct answer C. Zero
Why does a transformer not work with a steady direct current in its primary coil?
Correct answer B. Steady current produces a constant flux, so no emf is induced in the secondary
Why is the iron core of a transformer laminated?
Correct answer A. To reduce energy losses due to eddy currents
One tesla is the magnetic flux density in which ____.
Correct answer C. a 1 m wire carrying 1 A at right angles to the field experiences a force of 1 N
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The magnetic flux density inside a long current-carrying solenoid depends on which pair of quantities?
Correct answer A. Number of turns per unit length and current
A long solenoid has 2000 turns per metre and carries a current of 2.0 A. Take μ₀ = 4π × 10⁻⁷ T m A⁻¹. What is the magnetic flux density inside it?
Correct answer D. 5.0 × 10⁻³ T
A magnetic flux of 3.0 × 10⁻⁴ Wb passes normally through an area of 6.0 cm². What is the magnetic flux density?
Correct answer A. 0.50 T
A proton moves in a circle of radius 0.20 m in a uniform magnetic field of 0.50 T. Take mₚ = 1.67 × 10⁻²⁷ kg, e = 1.6 × 10⁻¹⁹ C. What is its speed?
Correct answer A. 9.6 × 10⁶ m/s
Magnetic flux density B can be described as ____.
Correct answer C. magnetic flux per unit area perpendicular to the field