Among the following the most suitable material for the core of an electro-magnet is
steel
wood
soft iron
copper
Correct Answer :
C. soft iron
Related Questions
When an electric bulb breaks, there la an explosive sound. That is due to
the chemical reaction between the gases inside the bulb
the compressed gases inside rushing out suddenly
the air outside rushing in to fill the vacuum inside the bulb
None of the above
Halley's comet appears in the heavens once in
40 years
50 years
76 years
80 years
You want a supply of a small but constant current. Which of the following cells will you prefer?
Daniell cell
Leclanche cell
Dry cell
All the above
Lightning is produced when
similar charges of electricity rush towards each other and then get repelled
clouds strike against impurities in air and the friction burns up these impurities
strong opposite charges in different clouds break down the resistance offered by the intervening air
water vapour produces electricity in the clouds
Atoms which have the same atomic number but different mass numbers are called
isobars
isomers
isotones
isotopes
Which physical quantity is measured in watts
power
kinetic energy
momentum
impulse
When a bullet is fired from a gun
the gun moves forward
the gun jumps up
the gun does not move
the gun recoils with the same momentum as the bullet
A pressure gauge for fluids is called
a hydrometer
a manometer
a lactometer
an anemometer
Which of the following is not electromagnetic waves?
heat waves
sound waves
radio waves
light waves
An ammeter has
a high resistance
a very low resistance
no resistance at all
resistance of 400 ? w
For detecting and, testing of small electric charges we use
an electrophorus
an electroscope
an electromagnet
an ammeter
Increase in pressure
increases the melting point of ice
decreases the melting point of ice
has no effect on the melting point of ice
increases the volume of the ice
In a refrigerator cooling is produced by
the ice that deposits on the freezer
the evaporation of a volatile liquid
None of the above
Both (a) and (b)
Formation of shadows can be explained by
rectilinear propagation of light
reflection
refraction
total internal reflection
Alpha particles are
electromagnetic radiations
helium nuclei
negatively charged particles
neutral particles
Heat transfer
cools the body that transfers it
heats the body that absorbs the heat
may change the physical state of the substance
All the above
A wire conveying a current deflects a pivoted magnetic needle. This was discovered by
Marconi
Oersted
Faraday
Ohm
Rain drops acquire spherical shape due to
viscosity
surface tension
friction
elasticity
You want a supply of a small but constant current. Which of the following cells will you prefer?
Daniell cell
Leclanche cell
Dry cell
All the above
The strength of an electromagnet can be increased by
increasing the length of the coiled wire
increasing current supply
increasing the size of the iron core
All the above
Increase in pressure
has no effect on the boiling point of a liquid
raises the boiling point of a liquid
lowers the boiling point of a liquid
increases the volume of a liquid
The stem of a vibrating tuning fork is pressed against a sound box. Then
the loudness of the sound increases
the loudness remains the same
the loudness decreases
the sound suddenly stops
A sensitive instrument susceptible to magnetic infiuence can be protected from external magnetic field by
enclosing it in a thick walled iron box
wrapping it with an insulator
by placing it inside a glass case
by surrounding it with fine copper gauze
Sound travels fastest in
air
water
iron
vacuum
At what temperature do the Fahrenheit and Celsius scales give the same reading?
212°
32°
-40°
0°
Mercury is used in a barometer because
its density being very high 13.6 g/cm3 the height of mercury column is conveniently small
at the ordinary temperature its vapour pressure is small
it is opaque and does not wet glass
All the above
Which part of the eye photographic camera?
Lens
Iris
Retina
Eyelid
The velocity required to place a vehicle in orbit round the moon is _________ that required to place it in orbit round the earth.
less than
greater than
equal to
greater than or equal to
Which of the following rays has the highest penetrative power?
a -rays
� -rays
? -rays
X-rays
Rays from the headlight of a motor car are rendered parallel by suitably using
a convex mirror behind it
a concave lens behind it
a concave mirror in front of it
a concave mirror behind it