BATTERY LIFE AND SIGNAL STRENGTH

Lower signal quality tends to use more battery. On standby if you lose signal, the phone will use more power trying to re-acquire a signal than it would with a constant signal. Also with a weaker signal the phone may have to retransmit more and therefore use more power that way.

Cell phones are limited to 1 watt maximum transmission power; but most of the time they use significantly less. If a phone is in a marginal area, it can maintain a signal by increasing the transmission power -- but it comes at the cost of a huge hit to battery life.


R.Isaac Sajan
A.P/CSE
Ponjesly College of Engineering

Electronics Quiz

POWER ELECTRONICS

[1] When a line commutated converter operates in the inverter mode
(a) It draws both real and reactive power from the AC supply
(b) It delivers both real and reactive power to the AC supply
(c) It delivers real power to the AC supply
(d) It draws reactive power from the AC supply
Answer: C
[2] A chopper operating at a fixed frequency is feeding an RL load. As the duty ratio of the chopper is increased from 25% to 75%, the ripple in the load current is
(a) Remains constant
(b) Decreases, reaches a minimum at 50% duty ratio and then increases
(c) Increases, reaches a maximum at 50% duty ratio and then decreases
(d) Keeps on increasing as the duty ratio is increased
Answer: A
[3] To turn off a SCR, the reverse bias should be applied for a period ....... the turn-off time of the SCR
(a) Equal to
(b) Longer than
(c) Less than
(d) Irrespective of
Answer: B
[4] In class A and class B commutation the resonating circuit has to be
(a) Over damped
(b) Critically damped
(c) Under damped
(d) Negatively damped
Answer: C
[5] In phase controlled rectification power factor (PF)
(a) Remains unaffected
(b) Improves with increase of firing angle α
(c) Deteriorates with increase of α
(d) Is unrelated to α
Answer: C
[6] Comparing with the full wave rectifier using two diodes, the four diode bridge rectifier has the dominant advantage of
(a) Higher current carrying
(b) Lower peak inverse voltage requirement
(c) Lower ripple factor
(d) Higher efficiency
Answer: B
[7] A SCR is rated at 75A peak, 20A average. The greatest possible delay in the trigger angle if the dc is at rated value is
(a) 47.5°
(b) 30° to 45°
(c) 74.5°
(d) 137°
Answer: B
[8] The applied sine voltage to a SCR is VM=200V and R=10Ohm. If the gate trigger lags the ac supply by 120°, the average load current is
(a) 15/π A
(b) 5/π A
(c) -5/π A
(d) -15/π A
Answer: A
[9] A sine voltage of 200Vrms, 50Hz is applied to an SCR through 100ohm resistor. The firing angle is 60°. Consider no voltage drop. The output voltage in rms is
(a) 89.7 V
(b) 126.7 V
(c) 166.7 V
(d) 200√2 V
Answer: B
[10] A 100VDC is applied to the inductive load through a SCR. The SCR's specified latching current is 100mA. The minimum required width of gating pulse to turn on the SCR is
(a) 100μS
(b) 100S
(c) 1mS
(d) 50μS
Answer: A
[11] A cycloconverter is a
(a) Frequency changer from higher to lower frequency with one-state conversion
(b) Frequency changer from higher to lower frequency with two-stage conversion
(c) Frequency changer from lower to higher frequency with one-stage conversion
(d) Either a or c
Answer: D
[12] The cycloconverter require natural or forced commutation as under
(a) Natural commutationin bothstep-up and step down cycloconverter
(b) Forced commutation in both step-up and step-down cycloconverter
(c) Forced commutation in step-up cycloconverter
(d) Forced commutation in step-down cycloconverter
Answer: C
[13] In synchronized UJT triggering of an SCR, voltage VC across capacitor reaches UJT threshold thrice in each half cycle so that there are three firing pulses during each half cycle. The firing angle of the SCR can be controlled
(a) Once in each half cycle
(b) Thrice in each half cycle
(c) Twice in each half cycle
(d) Four times in each half cycle
(e) None of the above
Answer: A
[14] In a GTO, anode current begins to fall when gate current
(a) Is negative peak at time t=0
(b) Is negative peak at t = storage period tS
(c) Just begins to become negative at t = 0
(d) Is negative peak at t = (tS + fall time)
Answer: B
[15] The SCR can be turned on by
(a) Applying anode voltage at a sufficiently fast rate
(b) Applying sufficiently large
(c) Increasing the temperature of SCR to a sufficiently large value
(d) Applying sufficiently large gate current
OPTIONS:
1) A, B
2) C, D
3) B, C
4) A, B, C, D
5) None of the above options
Answer: 4

Tech Quiz !!!

PONJESLY COLLEGE OF ENGINEERING

DEPARTMENT OF ECE

TECHNICAL QUIZ

Dear engineers, check how strong you are in your basics of electronics. The questions are given in a quiz form. So check how strong you are.

1. In a transistor when base-width decreases with increasing collector to base voltage, this phenomenon is called
   
   1. Early Effect
   2. Thermal Runaway
      
   3. Tunneling
      
   4. Pinch-off
      
2. The bridge used for measurement of inductance is
   
   1. Wheatstone Bridge
      
   2. Kelvin Double Bridge
      
   3. Anderson Bridge
      
   4. Schering Bridge
      
3. The type of transmission used for sound in TV transmission is
   
   1. AM
      
   2. FM
      
   3. PCM
      
   4. PWM
      
4. The type of transmission used for television in India is
   
   1. DAB SC
      
   2. SSB
      
   3. VSB
      
   4. SSB-SC
      
5. The memory unit using only gates is
   
   1. ROM
      
   2. RAM
      
   3. Core
      
   4. Disk
      
6. Most commonly used materials as photo cathode for the photoelectric emission are
   
   1. Barium and Calcium
      
   2. Cesium and Ribidium
      
   3. Arsenic and Boron
      
   4. Thorium and Tungsten
      
7. In every practical oscillator the loop gain is
   
   1. Slightly larger than unity
      
   2. Slightly larger than ten
      
   3. Infinity
      
   4. Zero
      
8. A series capacitance used in a filter circuit represents
   
   1. Low-Pass
      
   2. Band-Pass
      
   3. High-Pass
   4. None
      
9. Clipper circuits are used to obtain any one of the following waveforms
   
   1. Sharper
      
   2. Rectified
      
   3. Fast Rising
      
   4. Smaller Amplitude
      
10. Plasma is
    
    1. A medium dominated by helium
       
    2. A solid dielectric material
       
    3. A gaseous medium
       
    4. A ray of electrons
11. Which is most commonly used transmission-line with television system?
    
    1. Twin-lead
       
    2. Open-wire with ceramic supports
       
    3. Coaxial Cable
       
    4. None of these
       
12. Video signals have a frequency range that is spread over approximately
    
    1. 9 Octaves
       
    2. 18 Octaves
       
    3. 4 Octaves
       
    4. None of these
       
13. Where is brightness control located in a TV?
    
    1. Audio Section
       
    2. Video Section
       
    3. Grid-cathode circuit of picture tube
       
    4. None of these
       
14. LED is
    
    1. A PN junction which emits light when current passes in the forward direction
       
    2. A gaseous discharge glow devices
       
    3. Photo cell device which emits light
    4. None of the above
       
15. The oscillator that has the best frequency stability is
    
1. Crystal Oscillator
   
2. Hartley Oscillator
   
3. Colpitt's
   
4. Tuned Collector Oscillator
   

Answers: 1) a 2) c 3)b 4)c 5)b 6)c 7) a 8)c 9) d 10)c 11) c 12) c 13) a 14) a 15) a