function movePhotons(){
    i++;
    if (laserONFlag){
        var productionFactor = Math.ceil(1.5/ sim.calculation.getIntensity());
        if (i % productionFactor === 0){
            photon[++p] = new sim.lib.photon();
            // new photon is created
            photon[p].x = 40;
            photon[p].y = getRndInteger(-31, 31);
            // this is where the photon is created
            photons.addChild(photon[p]);
            // now the photon is ejected
            if (p > 10){p = 0;}
            Kmax = sim.calculation.getKmax(sim.currentElement) * 1.6e-19;
            // this is the maximum possible kinetic energy that the electron
            // that absorbs the photon may possess
            // and it depends on parameters contained in the class "Calculation"
            V0 = tubeLength * Math.sqrt(2 * Kmax / me) * 
            // this is the maximum possible initial velocity that an ejected electron can possess
            (sim.calculation.getLambda() < sim.calculation.getMaxLambda(sim.currentElement));
            // this is a condition: if the wavelength of the incident light beam is below the
            // threshold wavelength of the irradiated element, then an electron may be ejected,
            // otherwise, the energy of the incident photon is not enough for the electron to be
            // released 
            if (sim.calculation.calculateVoltageCoeff(sim.currentElement) === 1){
                v0 = V0;
                // this is when the photocurrent reaches a maximum value, called the saturation current
                // this happens when the potential of the anode plate is high enough
                // to pull all the released electrons and capture them
            } else {
                v0 = getRndNumber(0.7 * V0 , 1.01 * V0);
                // this allows for the fact that the electrons which absorb photons will be ejected
                // with kinetic energy of maximum value V0 that is calculated above (here the randomization
                // between 0.7 * V0 and 1.01 * V0 is not realistic but to allow an adequate visualization
                // for educational purpose only)
                // So probability plays a role here.
            }
            i = 0;
        }
    }
    for (p in photon){
        photon[p].x += 5;
        if (photon[p].x > (380 + photon[p].y * Math.tan(beamAngle))){
            // if a photon reaches the plate
            if (getRndNumber(0,1) > 0.5){
                // Another probabilistic factor here allows for the fact not all the photons hitting
                // the plate get caught and cause the ejection of electrons
                // So probability plays a role here too
                // Note that the speed of photons and electrons in the tube in this simulation and the
                // number of photons that cause ejection of electrons are not accurate but tuned to be
                // clearly visualized so that the learners understand the concept visually.
                electron[++m] = new sim.lib.electron();
                // the electron that absorbed the incident photon and
                // gained enough energy and got lucky to escape from the
                // surface of the plate..
                electron[m].x = -8;
                electron[m].y = photon[p].y / Math.cos(beamAngle);
                // ..starts from the surface of the plate..
                electron[m].alpha = 0.6;
                electron[m].v = v0;
                // ..with an initial speed previously calculated..
                electron[m].v0 = v0;
                electrons.addChild(electron[m]);
                // ..and hence flies away!
            }
            photons.removeChild(photon[p]);
            delete photon[p];
            // .. and don't forget that the incident photon vanished
            // since it is absorbed by the electron!
            if (p > 4){p = 0;}
        }
    }
}

function moveElectrons(){
    // Now the electron is flying
    for (m in electron){
        // for every electron which was released from the platee..
        a = (voltageONFlag) * e * sim.calculation.getVoltage() / (me * tubeLength);
        // ..this is its acceleration due to electrostatic force on it
        // caused by the potential difference between the cathode and the anode.
        // notice that when the power supply is off, the flag "voltageONFlag" is
        // false (false is equivalent to 0), so a = 0 (since there is no potential 
        // difference anymore), and hence, the electron is not accelerating 
        electron[m].v += 0.5 * a;
        // this is how much the speed of the electron is increasing (depending on a, the 
        // acceleration)
        // note that if a is zero, then the speed of the electron becomes constant
        electron[m].x -= 2.0e-9 * electron[m].v;
        // this is how fast the electron is moving (depending on the speed)
        // if the speed is constant, then the motion of the electron is uniform,
        // while if the speed is increasing, then the electron is accelerating
        // (remember that this happens when a potential difference is applied between the plates)
        if (electron[m].x < -440 || electron[m].x > -8){
            // if the electron reaches the anode plate
            electrons.removeChild(electron[m]);
            delete electron[m];
            // the electron disappears since it is being absorbed by the anode plate!
            if (m > 4){m = 0;}
        }
    }
}