C. Should be the answer it worked for me
Here observer is moving along with an electrical charge
now magnetic field on a moving charge is given by equation

electrical force on a moving charge is given by formula

so here we can say when observer is moving with the charge it will have two forces on it
1. magnetic force due to existing magnetic field
2. electric force due to electric field
so here he must have to experience both type of field presence
So here correct answer must be
<em>C- electric and magnetic fields </em>
A boiling pot of water (the water travels in a current throughout the pot), a hot air balloon (hot air rises, making the balloon rise) , and cup of a steaming, hot liquid (hot air rises, creating steam) are all situations where convection occurs.
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The terminal speed of the marble is 0.588 m/s.
<h3>Calculation:</h3>
We know that,
F = mg ......(1)
where,
F = force
m = mass
g = acceleration due to gravity
Also,
v = F/k ......(2)
where,
v = terminal speed
k = proportionality constant
Substituting the value of F from equation (1) in equation (2)
v = mg/k .......(3)
Given,
m = 30 g = 0.030 kg
k = 0.500 kg/s
g = 9.8 m/s²
To find,
v =?
Put the values in equation (3)
v = mg/k
v = 0.03(9.8)/ 0.500
= 0.294/0.500
= 0.588 m/s
Hence, the terminal speed of the marble is 0.588 m/s.
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