Answer:
Option D: Four times the original speed.
Explanation:
A centripetal force accelerates a body by changing the direction of the body's velocity without changing the body's speed.
The speed(v) is therefore constant, thereby making the magnitudes of the of the acceleration and the force constant.
The formula used to calculate the Centripetal force is given below:

where F represents the Centripetal force, m represents the mass of the moving body, v represents the speed or velocity at which the body is moving and r represents the radius.
Making the speed the subject of the formula: 
Therefore, when the radius (r) is changed to 4r, i.e r = 4r
speed(v) becomes 
After comparing, the difference between the speeds is Four times the original speed.
d. natural gas is the answer
The curved surface of water is called the meniscus
Answer:
Explanation:
The wires are in circular shape . They have common center .
magnetic field due to circular wire is given by the formula
B = 
where I is current , r is radius of the coil .
magnetic field due to inner wire
= 
magnetic field due to outer wire
= 
These should be equal and opposite so that by cancelling each other , they create zero field.
= 
I = 16.66 A
Direction of current should be in opposite direction ie anticlockwise when looking from above.
Radio waves are the lowest level of waves