Let us consider a copper wire having radius r and length l. Let its resistance be R. If the radius of another copper wire is 2r and the length is $$\frac{l}{2}$$, then the resistance of this wire will be

A mobile phone charger is

A. an inverter

B. a ups

C. a step up transformer

D. a step down transformer

What will be the total resistance of the three 20-Ω coils connected in series?

A. 40 Ω

B. 20 Ω

C. 60 Ω

D. 800 Ω

AC and DC are the form of?

A. charge flow

B. voltage flow

C. water flow

D. air flow

Superconductors are substances which

A. conduct electricity at lower temperature

B. offer high resistance to the flow of current

C. offer not resistance to the flow of current

D. conduct electricity at high temperature