Make two toy telephones. Use them as shown in Fig. 13.20. Make sure that the two strings are taut and touch each other. Let one of you speak. Can the remaining three persons hear? See how many more friends you can engage in this way. Explain your observations.
Answers
Answer:
A current element is a conductor carrying current.It is the product of current,I and length of very small segment of current carrying wire ,dL.
Let us consider a small element AB of length dl of the conductor RS carrying a current I.
Let r be the position vector of the point P from the current element I dL.and θ be the angle dl and r.
According to Biot-Savarts law,the magnetic field induction dB or magnetic flux density at a point P due to current element depends upon the following factors.
(i) dBI
(ii) dBdl
(iii) dBsinθ
(iv) dB1/r^2
Combining these factors,we get
dBIdLsinθ/r^2
or dB=K Idl sinθ/r^2
where K is a constant of perportionality.
In S.I units, K=μ0/4
thus , dB=μ0/4 I dl sinθ/r^2
where μ0 is absolute premeability of free space and
μ0=4*10^-7 Wb A^-1m^-1
= 4*10^-7*TA^-1m [ 1T=1 Wb m^-2]
In C.G.S units,K=1 (In free space)
Thus dB=Idl sinθ/r^2
In vector form,
dB=μ0/4 I(dl*r)/r^3
magnetic field induction at point P due to current through entire wire is
B=∫μ0/4Idl*r/r^3
Or B=∫μ0/4 Idl sin θ/r^2
Answer:
Yes remaining 3 person can hear if the knot will be tight and strings would touch each other properly.
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