The diagram above shows the magnetic field around a bar magnet which has its N-pole pointing north. The neutral points in the field are likely to occur at
A negatively charged rod is brought near the cap of a gold-leaf electroscope. The cap is earthed momentarily while the rod is near to it. The rod is then removed. Which of the following is correct?
A.
The cap will be positively charged and the negatively charged leaves will diverge
B.
The cap will be negatively charged and the positively charged leaves will diverge
C.
The cap and the leaves will be positively charged
D.
The cap and the leaves will be negatively charged.
E.
The leaves will not diverge because the cap has been earthed.
Calculate the length of a constantan wire of cross- sectional area 4 π x 10-8m2 and resistivity 1.1 x 10-6 Ω m required to construct a standard resistor of resistance 21 Ω. [Take π = 22/7]
