The voltage and current in the primary of a transformer are 200V and 2Arespectively. lf the transformer is used to light ten 12 V, 30 W bulbs, calculate its efficiency.
A100%
B90%
C75%
D50%
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Question 642
waec1999
Magnetic flux density is defined as the
Atotal number of magnetic lines of force surrounding a magnet
Bnumber of magnetic lines of force per unit area normal to the magnetic field
Cstrength of the magnetic field surrounding a current-carrying conductor
Dmagnetic force exerted on a unit magnetic pole
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Question 643
waec1999
A resistance wire of length 2 m and of uniform cross-sectional area 5.0 x 10-7 m2 has a resistance of 2.2 Ω Calculate its resistivity
A1.8 x 10-7Ωm
B5.5 x 10-7Ωm
C1.8 x 10-7Ωm
D5.8 x 107Ωm
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Question 644
waec1999
The parts of a bar magnet at which the magnetic effect is strongest are called the
Apoles
Bneutral points
Cmagnetic declinations
Dmagnetic meridians
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Question 645
waec1999
Using the diagram above, calculate the effective capacitance of the circuit
A1.56μf
B3.00μF
C3.71μF
D9.00μF
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Question 646
waec1999
Using the data on the diagram above, calculate the potential difference across the 20- Ω resistor. (Neglect the internal resistance of the cell)
A5V
B10V
C20V
D60V
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Question 647
waec1999
Thunder is usually heard some seconds after lightning is observed because
Athe human eye is more sensitive to light than the ear to sound
Bsound and light travel in different media
Cthunder occurs after lightning
Dlight travels faster than sound
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Question 648
waec1999
If the position of resonance in a resonance tube is 16.50cm from open end of the tube, calculate the distance from the open end to the next position where resonance occurs. (Neglect end-correction)
A24.75cm
B33.00cm
C41.25cm
D49.50cm
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Question 649
waec1999
ln order to obtain a sound note of a high pitch from a wire stretched by a constant tension, the wire must be
Ashort and thick
Bshort and thin
Clong and thick
Dlong and thin
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Question 650
waec1999
The amplitude of a wave is the
Adistance between two successive troughs of the wave
Bseparation of two adjacent particles vibrating in phase
Cmaximum displacement of the wave particle from the equilibrium position
Ddistance travelled by a wave in a complete cycle of its motion
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Question 651
waec1999
Which of the following statements is not correct about long sight?
AA Iong-sighted person can see distant objects clearly
Bight from a nearby object is focused behind the retina.
CThe eyeball is too short
DThe defect is corrected by using a diverging lens.
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Question 652
waec1999
The real image of an object formed by a converging lens of focal length 15cm, is three times the size of the object. Calculate the object distance
A60cm
B30cm
C20cm
D15cm
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Question 653
waec1999
The refractive index of glass for yellow light is greater than that for red light because yellow light
Ahas a greater amplitude than red light
Bis more intense than red light
Ctravels more slowly than red light
Ddeviates less than red light
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Question 654
waec1999
The image of an object is located 6cm behind a convex mirror. If its magnification is 0.6, calculate the focal length of the mirror
A3.75cm
B6.60cm
C10.00cm
D-15.00cm
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Question 655
waec1999
The air column in a resonance tube is set into resonance by a vibrating tuning fork. The resultant waves in the air column will be
Amechanical and transverse
Bprogressive and longitudinal
Cstationary and transverse
Dstationary and longitudinal.
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Question 656
waec1999
A ray of light is incident on 'a plane mirror at an angle of 20o. This mirror is rotated through, twice this angle, In this new position the angle between the incident ray and the reflected ray is
A20o
B40o
C80o
D120o.
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Question 657
waec1999
Calculate the power rating of an immersion heater used for 10 minutes to increase the temperature of 10kg of water by 15K. (Specific heat capacity of water = 4200 J l
A1,050W
B16,800W
C18,060W
D20,160W
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Question 658
waec1999
Which of the following statements about evaporation is not correct?
AThe rate of evaporation of a liquid varies with temperature
BThe molecules of an evaporating liquid have an average speed
CEvaporation occurs when faster molecules escape from the surface of a liquid
DEvaporation takes place inside a liquid.
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Question 659
waec1999
Calculate the heat energy required to change 0.1kg of ice at 0oC to water boiling at 100oC. (Specific heat capacity of water = 4200 J kg-1K-1) (Specific latent heat of fusion of ice = 336,000 J kg-1)
A75,600J
B336,000J
C340,200J
D378,000J.
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Question 660
waec1999
Which of the following statements is not correct?
AA sea breeze is due to convection in air
BCotton materials are better than woollen ones for use in hot weather
CConvectional currents play an important role in the cooling of the engine of a motor car
DThe vacuum space in a flask helps to reduce heat loss by radiation.
