The velocity-time graphs of two particles moving in a straight line are shown in the adjoining figure.
(i) Which of the two particles has greater acceleration and how much?
(ii) Calculate the difference between the distances traveled by the particles in 10 seconds
Answers
Explanation:
distance travelled = area under v-t curve
at 4s distance= 4×20= 80m
in this case the acceleration of the particle = slope= 5/1= 5m/s^2
Now velocity at 5s = u+at = 0+5×5 =25m/s
from the graph we can see that at 3 s the velocity of the particle is 15m/s
Answer:
To find the relationship between current and drift velocity, consider a conductor of length l and area of cross-section A. If V is the potential difference across the ends of the conductor, then the strength of the electric field is
The acceleration acquired by each electron due to the electric field is
where is the coulomb's force experienced by each electron and m is the mass of the electron.
The drift velocity of the electrons is given by
where t, the relaxation time, is the average time that an electron spends between two collisions. It is of the order of 10-14 s.
Now the volume of the conductor is equal to Al and if n is the number of free electrons per unit volume, then, the total number of free electrons in the conductor will be equal to n Al.
Hence, the total charge q = - n Ale
The time taken by free electrons to cross the conductor is
where we have substituted for t and q.
For a given conductor, I a Vd
A small value of drift velocity 10-5m/sec produces a large amount of current, as there are a large number of free electrons in a conductor.
The drift velocity of the electrons Vd is (using E = V / l)
Also I = - neAVd
On substituting for Vd in the above expression we get,
or
Which shows that current is directly proportional to the applied voltage(Ohm's law).From this, the resistance R can be identified as