CSIR Physical Sciences: Questions 134 - 137 of 401

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Question number: 134

» Electromagnetic Theory » Gauss Law and Applications

Appeared in Year: 2014

MCQ▾

Question

A solid of radius R has a charge density, given by ρ(r)=ρ0(1arR) ; where r is the radial coordinate and ρ0 and R are positive constants. If the magnitude of the electric field at r=R2 is 1.25 times that at r=R, then the value of a is – (December)

Choices

Choice (4) Response

a.

2

b.

14

c.

1

d.

12

Question number: 135

» Electronics and Experimental Methods » Opto-Electronic Devices » LEDs

Appeared in Year: 2012

MCQ▾

Question

An LED operates at 1.5 V and 5 mA in forward bias. Assuming an 80 % external efficiency of the LED, how many photons are emitted per second? (June)

Choices

Choice (4) Response

a.

1.5×1016

b.

2.5×1016

c.

0.8×1016

d.

5.0×1016

Question number: 136

» Electronics and Experimental Methods » Semiconductor Devices » Transistors

Appeared in Year: 2012

MCQ▾

Question

The transistor in the given circuit has hfe=35Ω and hie=1000Ω . If the load resistance RL=1000Ω , the voltage and current gain are, respectively – (June)

Circuit diagram of transistor

Circuit Diagram of Transistor

In figure a circuit consist of the transistor is shown.

Choices

Choice (4) Response

a.

+35and35

b.

35and0.97

c.

0.98and35

d.

35and+35

Question number: 137

» Electromagnetic Theory » Magnetostatics » Ampere's Theorem

Appeared in Year: 2013

MCQ▾

Question

A horizontal metal disc rotates about the vertical axis in a uniform magnetic field pointing up as shown in the figure. A circuit is made by connecting one end A of a resistor to the centre of the disc and the other end B to its edge through a sliding contact S. The current that flows through the resistor is – (December)

A rotating horizontal metal disc

A Rotating Horizontal Metal Disc

In figure a horizontal metal disc rotates about the vertical axis in a uniform magnetic field pointing up is shown. A circuit is made by connecting one end A of a resistor to the centre of the disc and the other end B to its edge through a sliding contact S.

Choices

Choice (4) Response

a.

DC from A to B

b.

Zero

c.

DC from B to A

d.

AC

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