1
JEE Main 2021 (Online) 17th March Evening Shift
+4
-1
Two cells of emf 2E and E with internal resistance r1 and r2 respectively are connected in series to an external resistor R (see figure). The value of R, at which the potential difference across the terminals of the first cell becomes zero is

A
r1 $$-$$ r2
B
$${{{r_1}} \over 2} - {r_2}$$
C
$${{{r_1}} \over 2} + {r_2}$$
D
r1 + r2
2
JEE Main 2021 (Online) 17th March Evening Shift
+4
-1
The four arms of a Wheatstone bridge have resistances as shown in the figure. A galvanometer of 15$$\Omega$$ resistance is connected across BD. Calculate the current through the galvanometer when a potential difference of 10V is maintained across AC.

A
4.87 $$\mu$$A
B
4.87 mA
C
2.44 mA
D
2.44 $$\mu$$A
3
JEE Main 2021 (Online) 17th March Morning Shift
+4
-1
A current of 10A exists in a wire of cross-sectional area of 5 mm2 with a drift velocity of 2 $$\times$$ 10$$-$$3 ms$$-$$1. The number of free electrons in each cubic meter of the wire is ___________.
A
625 $$\times$$ 1025
B
1 $$\times$$ 1023
C
2 $$\times$$ 1025
D
2 $$\times$$ 106
4
JEE Main 2021 (Online) 16th March Evening Shift
+4
-1
A resistor develops 500 J of thermal energy in 20 s when a current of 1.5A is passed through it. If the current is increased from 1.5A to 3A, what will be the energy developed in 20 s.
A
1000 J
B
2000 J
C
1500 J
D
500 J
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