1. An oscilloscope input impedance consists of I M W in parallel with 100pF. A compensated 20: 1 attenuator is obtained by connecting a parallel combination of

(a) 19 M W and pF (b) 20 M W and pF

(c) 19 M W and 1900 pF (d) 20 M W and 2000 pF.

2. The bridge circuit in Fig. 1.17 is balanced. The magnitude of current I is

• 2mA
• 4mA
• 5mA
• 6mA

3. A phase locked loop can be employed for demodulation of

(a) pulse amplitude modulated signals

(b) pulse code modulated signals

(c) frequency modulated signals

(d) single side band amplitude modulated signals.

4. A number in 4-bit two's complement representation is X 3 X 2 X 1 X o . This number when stored using 8-bi1s will be

(a) 0000 X 3 X 2 X 1 X o

(b) 1111 X 3 X 2 X 1 X o

(c) X 3 X 3 X 3 X 3 X 3 X 2 X 1 X o

(d) X 3 X 2 X 1 X o

5. A computer has a memory space of 2 16 and word length of 24 bits. The memory chips available have 10 address and 8 data lines. The number of chips required for the computer memory space is

(a) 192 (b) 256

(c) 512 (d) 1024

6. For a shaft encoder, the most appropriate 2-bit code is

(a) 11,10,01,00 (b) 11,10,00,01

(c) 01, 10, 11,00 (d) 01,00, 11, 10

7. The term 'precision' used in instrumentation means

(a) gradual departure of the measured value from the calibrated value

(b) smallest increment in the measure and that can be detected by the instrument

(c) maximum distance or angle through which any part of a mechanical system may be moved in one direction without causing motion of the next part

(d) the ability of the instrument to give output readings close to each other, when the input is constant.

8. A resistance potentiometer has a total resistance of 10000 W and is rated 4 W. If the range of potentiometer is 0 to 100 mm, then its sensitivity in V/mm is

(a) 1.0 (b) 2.0

(c) 2.5 (d) 25

9. The temperature of fixed points used to define International Temperature Scale are determined by using

(a) Platinum resistance thermometer

(b) Platinum, Platinum-Rhodium thermo-couples

(c) vapour-pressure thermometer

(d) gas thermometer to which corrections are applied for non-ideal behaviour of the gas.

10.The emf-temperature data for a thermocouple with reference junction at O°C is as follows,

Temperature ( 0C) 20 180 200

emf(mV) 1.2 11.8 13.5

The emf developed in mV with the two junctions at 200°C is

(a) 11.8 (b) 12.3

(c) 13.0 (d) 13.5

11. A rotameter with a heavy float for measuring gas flow is calibrated with a gas of density 1.2 kg/m 3. It measures the flow rate of a different gas having density of 2 kg/m 3 and indicates a flow rate of 2.2 m 3/min. The actual flow rate in m 3/min is

(a) 0.79 (b) 1.32

(c) 1.70 (d) 2.20

12.The sound pressure level (SPL) measured in open space (free field), at a distance of 6 m from a noise source is 80 dB. At a distance of 60 m, the SPL is

(a) 80 dB (b) 60 dB

(c) 8 dB (d) 1.34 dB

13. An optical fibre has a refractive index of 1.641 for the core and 1.422 for the cladding. The critical angle above which a ray will be totally internally reflected is

(a) 37 o (b) 41°

(c) 45° (d) 60°

14. A frequency stablised HeNe laser with a wavelength of 6328 A 0 has a bandwidth of 1 MHz. Its coherence length is

• 0.3 m
• 3 m
• 30 m
• 300 m

15. Attenuation of a narrow monochromatic X-ray beam in a metal plate of thickness 'd' is given by the equation

(a) I=I o exp(- m d)

(b) I= I 0 exp (- m d 2)

(c) I = I 0 exp (- m /d)

(d) I= I 0 exp (- m /d 2)