સોહેલ ખાન : મલાયકા અરોર :: સૈફ અલી ખાન : ??

A single phase 240 V, 1 kW heater is connected across single phase 240 V, 50 Hz supply through an SCR. For firing angle delay of 90˚, calculate the power absorbed in the heater element.

Resistance of heater, R = V²/P
R = 57.6 ohm

RMS value of voltage through controlled SCR = (Vm/2π)*(1 + cosα)
= 120 V

Power absorb by heater = Vrms²/R
= 120²/57.6
= 250 W

નીચે માંથી ક્યાં રુઢિપ્રયોગનો અર્થ 'છેતરવું' એવો થાય

The voltage applied to a transformer primary is increased keeping V/f constant. With this, the core loss ____ and the magnetizing current (Im) ____

For trasnformer:
1. e = 4.44fφ*Turns
2. V/f ≈ e/f ∝ φ ∝ B
3. Eddy Current loss, Pe ∝ B²f² ∝ f² (as B is constant if V/f is constant)
4. Hysteresis loss, Ph ∝ B^1.6*f ∝ f
If V/f is constant, B is constant, mmf required to create B is constant, Im is constant.

The relation between electric intensity E, voltage applied V and the distance d between the plates of a parallel plate condenser is

The relation between electric intensity E, voltage applied V and the distance d between the plates of a parallel plate condenser is given by:
V = E*L
E = V/L

A three-phase 400 V, 6-pole, 50 Hz squirrel-cage induction motor is running at a slip of 5%. The speed of rotor with respect to stator magnetic field and speed of the stator magnetic field with respect to rotor magnetic field are

Slip, s = (Ns - Nr)/Ns
Ns = 120f/P
0.05 = (1000 - Nr)/1000
Nr = 950 rpm
Speed of rotor with respect to stator magnetic field = 950 - 1000 = -50 rpm

Speed of the stator magnetic field with respect to stator core = 0
Speed of the rotor magnetic field with respect to rotor = sNs
Speed of the stator magnetic field with respect to rotor magnetic field = 0
Speed of the rotor magnetic field with respect to stator core = Ns