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WBCHSE HS Vocational Power study materials
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WBCHSE HS Vocational Power practice questions

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Question 1Basic Electrical Principles and Circuit Fundamentals

In a simple DC circuit, what is the standard unit of electrical resistance?

  1. Volt
  2. Ampere
  3. Ohm Correct answer.
  4. Watt

Explanation

Resistance is measured in ohms, with the symbol Ω. It expresses how strongly a component opposes the flow of current for a given applied voltage.

Question 2Basic Electrical Principles and Circuit Fundamentals

A resistor of 20 Ω carries a current of 3 A. What is the potential difference across it?

  1. 60 V Correct answer.
  2. 6.67 V
  3. 23 V
  4. 0.15 V

Explanation

Ohm's law states that V = I × R. Multiplying 3 A by 20 Ω gives 60 V across the resistor.

Question 3Basic Electrical Principles and Circuit Fundamentals

Which material is the best conductor of electricity among the following?

  1. Glass
  2. Dry wood
  3. Copper Correct answer.
  4. Rubber

Explanation

Copper has many free electrons and therefore very low resistivity, making it an excellent conductor. Glass, rubber and dry wood are insulators with very few free charge carriers.

Question 4Basic Electrical Principles and Circuit Fundamentals

Two resistors of 6 Ω and 3 Ω are connected in series. What is the total resistance of the combination?

  1. 18 Ω
  2. 4.5 Ω
  3. 2 Ω
  4. 9 Ω Correct answer.

Explanation

In a series circuit the same current passes through each element and the resistances simply add. Thus 6 Ω + 3 Ω gives a total of 9 Ω.

Question 5Basic Electrical Principles and Circuit Fundamentals

What is the total resistance of a 4 Ω and a 4 Ω resistor connected in parallel?

  1. 16 Ω
  2. 8 Ω
  3. 4 Ω
  4. 2 Ω Correct answer.

Explanation

For two equal resistors in parallel the equivalent resistance is half of one value, so 4 Ω in parallel with 4 Ω gives 2 Ω. The reciprocal formula 1/R = 1/4 + 1/4 confirms this.

Question 6Basic Electrical Principles and Circuit Fundamentals

Which instrument is connected in series with a circuit branch to measure the current through it?

  1. Wattmeter
  2. Megger
  3. Ammeter Correct answer.
  4. Voltmeter

Explanation

An ammeter is placed in series so that the branch current passes through it, and it is designed to have very low resistance. A voltmeter, by contrast, is connected in parallel across the component.

Question 7Basic Electrical Principles and Circuit Fundamentals

In a circuit, what does an electromotive force (emf) of a cell represent?

  1. The resistance inside the connecting wires
  2. The rate at which charge leaves the cell
  3. The total charge stored in the cell
  4. The energy supplied per unit charge by the source Correct answer.

Explanation

Emf is defined as the energy converted from non-electrical to electrical form per unit charge driven around the circuit. It is measured in volts, the same unit as potential difference.

Question 8Basic Electrical Principles and Circuit Fundamentals

A 12 V supply is connected across a 4 Ω resistor. What power is dissipated in the resistor?

  1. 36 W Correct answer.
  2. 48 W
  3. 3 W
  4. 0.33 W

Explanation

Power can be found from P = V²/R. Substituting gives 144 divided by 4, which equals 36 W dissipated as heat in the resistor.

Question 9Basic Electrical Principles and Circuit Fundamentals

A current of 0.5 A flows for 2 minutes. How much charge passes a point in the circuit?

  1. 60 C Correct answer.
  2. 0.25 C
  3. 240 C
  4. 1 C

Explanation

Charge equals current multiplied by time, Q = I × t. Two minutes is 120 s, so 0.5 A × 120 s gives 60 C.

Question 10Basic Electrical Principles and Circuit Fundamentals

Three resistors of 2 Ω, 3 Ω and 5 Ω are in series across a 20 V supply. What is the current in the circuit?

  1. 4 A
  2. 2 A Correct answer.
  3. 0.5 A
  4. 10 A

Explanation

The series resistance is 2 + 3 + 5 = 10 Ω. Using I = V/R gives 20 V divided by 10 Ω, which is 2 A, and this same current flows through every resistor.

Question 11Basic Electrical Principles and Circuit Fundamentals

A 6 Ω and a 3 Ω resistor are connected in parallel across a 12 V supply. What current flows from the supply?

  1. 1.33 A
  2. 6 A Correct answer.
  3. 4 A
  4. 18 A

Explanation

The parallel equivalent is (6 × 3)/(6 + 3) = 2 Ω. The supply current is then 12 V divided by 2 Ω, which equals 6 A.

Question 12Basic Electrical Principles and Circuit Fundamentals

Kirchhoff's current law applied to a junction states that the algebraic sum of currents is zero. What does this express in physical terms?

  1. Resistance is zero at the junction
  2. Energy is dissipated at the junction
  3. Charge is conserved at the junction Correct answer.
  4. Voltage rises across the junction

Explanation

Kirchhoff's current law follows from conservation of charge: charge cannot accumulate at a node, so the total current entering equals the total leaving. The algebraic sum of all currents at the node is therefore zero.

Question 13Basic Electrical Principles and Circuit Fundamentals

Kirchhoff's voltage law is applied around a closed loop of a DC circuit. Which statement correctly describes it?

  1. The total resistance around the loop is zero
  2. The sum of currents around the loop is zero
  3. The algebraic sum of emfs equals the algebraic sum of potential drops Correct answer.
  4. The power in each element is equal

Explanation

Kirchhoff's voltage law reflects conservation of energy: as charge travels once around a closed loop, the energy gained from sources equals the energy lost in the passive elements. Hence the sum of emfs equals the sum of potential drops.

Question 14Basic Electrical Principles and Circuit Fundamentals

Two cells of 1.5 V each are connected in series aiding to a 3 Ω resistor. What current flows, ignoring internal resistance?

  1. 1 A Correct answer.
  2. 4.5 A
  3. 3 A
  4. 0.5 A

Explanation

In series aiding the emfs add, giving a total of 3 V. Dividing by the 3 Ω resistance gives 1 A through the circuit.

Question 15Basic Electrical Principles and Circuit Fundamentals

A wire of resistance 8 Ω is stretched uniformly to twice its original length. Assuming resistivity and volume stay constant, what is its new resistance?

  1. 8 Ω
  2. 16 Ω
  3. 32 Ω Correct answer.
  4. 4 Ω

Explanation

Stretching to double length halves the cross-sectional area, since volume is constant. Resistance varies as length divided by area, so it increases by a factor of four, giving 32 Ω.

Question 16Basic Electrical Principles and Circuit Fundamentals

Which statement correctly describes the resistance of a metallic conductor as its temperature rises?

  1. Resistance increases because lattice vibrations scatter electrons more Correct answer.
  2. Resistance falls to zero at ordinary temperatures
  3. Resistance stays constant for all metals
  4. Resistance decreases because more free electrons appear

Explanation

In metals, heating increases the amplitude of lattice vibrations, so electrons are scattered more often and resistance rises. This is why the temperature coefficient of resistance for metals is positive.

Question 17Basic Electrical Principles and Circuit Fundamentals

A battery of emf 12 V with internal resistance 1 Ω supplies a 5 Ω external resistor. What is the terminal voltage of the battery?

  1. 2 V
  2. 6 V
  3. 12 V
  4. 10 V Correct answer.

Explanation

The total resistance is 6 Ω, so the current is 12/6 = 2 A. The internal drop is 2 A × 1 Ω = 2 V, so the terminal voltage is 12 − 2 = 10 V.

Question 18Basic Electrical Principles and Circuit Fundamentals

In a two-resistor voltage divider, 10 Ω and 20 Ω are connected in series across 30 V. What is the voltage across the 20 Ω resistor?

  1. 15 V
  2. 20 V Correct answer.
  3. 10 V
  4. 30 V

Explanation

The current is 30 V divided by 30 Ω, which is 1 A. The voltage across the 20 Ω resistor is then 1 A × 20 Ω = 20 V, i.e. two-thirds of the supply.

Question 19Basic Electrical Principles and Circuit Fundamentals

A 100 W, 250 V lamp is operated at its rated voltage. What current does it draw and what is its resistance?

  1. 0.25 A and 1000 Ω
  2. 0.4 A and 250 Ω
  3. 0.4 A and 625 Ω Correct answer.
  4. 2.5 A and 100 Ω

Explanation

From P = V × I, the current is 100/250 = 0.4 A. The resistance follows from R = V/I = 250/0.4 = 625 Ω, which can also be found from V²/P.

Question 20Basic Electrical Principles and Circuit Fundamentals

In a domestic wiring circuit, which conductor is intended to carry current only under fault conditions?

  1. The phase conductor
  2. The live conductor
  3. The neutral conductor
  4. The earth (protective) conductor Correct answer.

Explanation

The earth conductor normally carries no current and provides a low-resistance path to ground during a fault, allowing protective devices to operate. Live and neutral conductors carry the operating current.

Question 21Basic Electrical Principles and Circuit Fundamentals

A network has two parallel branches between nodes A and B: one branch is 4 Ω and the other is 6 Ω. A 2 Ω resistor is then connected in series with this parallel combination. What is the total resistance between the ends?

  1. 3.2 Ω
  2. 5 Ω
  3. 12 Ω
  4. 4.4 Ω Correct answer.

Explanation

The parallel pair gives (4 × 6)/(4 + 6) = 2.4 Ω. Adding the series 2 Ω resistor gives 4.4 Ω in total.

Question 22Basic Electrical Principles and Circuit Fundamentals

A 12 V source with 2 Ω internal resistance feeds a load. At what load resistance is maximum power transferred to the load?

  1. 12 Ω
  2. 0 Ω
  3. 6 Ω
  4. 2 Ω Correct answer.

Explanation

The maximum power transfer theorem states that the load receives maximum power when its resistance equals the source's internal resistance. Here the internal resistance is 2 Ω, so the load should also be 2 Ω.

Question 23Basic Electrical Principles and Circuit Fundamentals

A coil draws 2 A at 230 V and dissipates 230 W. What is its effective resistance, neglecting other effects?

  1. 57.5 Ω Correct answer.
  2. 230 Ω
  3. 115 Ω
  4. 28.75 Ω

Explanation

Power in a resistive element is I²R, so R = P/I² = 230/4 = 57.5 Ω. Equivalently, the resistive voltage drop is P/I = 115 V and R = 115/2.

Question 24Basic Electrical Principles and Circuit Fundamentals

Two resistors, 6 Ω and 12 Ω, are in parallel and the combination is connected across a 24 V supply. What is the total power drawn from the supply?

  1. 144 W Correct answer.
  2. 48 W
  3. 32 W
  4. 96 W

Explanation

The parallel equivalent is (6 × 12)/(6 + 12) = 4 Ω. Total power is V²/R = 576/4 = 144 W, which also equals the sum of the branch powers 96 W and 48 W.

Question 25Electrical Wiring, Cables and Installation Practice

In a domestic single-phase wiring installation, which conductor is identified by insulation that is solid green or green with yellow stripes?

  1. The phase conductor
  2. The two-way switch traveler conductor
  3. The neutral conductor
  4. The protective earth conductor Correct answer.

Explanation

Indian wiring convention, followed by IS 732, reserves solid green or green-with-yellow insulation exclusively for the protective earth conductor. This conductor bonds exposed metalwork to the earth electrode so that fault current trips the protective device.

Question 26Electrical Wiring, Cables and Installation Practice

A copper conductor of a lighting circuit is specified as 1.5 sq mm. What does this figure describe?

  1. The diameter of the conductor in millimetres
  2. The cross-sectional area of the conductor Correct answer.
  3. The overall diameter of the insulated cable
  4. The current rating of the conductor in amperes

Explanation

Cable sizes such as 1.5 sq mm, 2.5 sq mm and 4 sq mm state the nominal cross-sectional area of the metal conductor in square millimetres. Current-carrying capacity is then read from cable-rating tables for that area and installation method.

Question 27Electrical Wiring, Cables and Installation Practice

Which wiring system is specified for a workshop where corrosive chemical vapours are present and the wiring must be mechanically strong and vapour-tight?

  1. Conduit wiring using rigid steel conduit with sealed joints Correct answer.
  2. Temporary flexible wire laid on the floor
  3. PVC conduit wiring on wooden battens
  4. Cleat wiring with porcelain cleats

Explanation

Rigid steel conduit gives mechanical protection and, when all joints and boxes are sealed, resists ingress of corrosive vapour. Cleat and batten wiring leave conductors exposed, and loose flexible cable is both unsafe and non-compliant.

Question 28Electrical Wiring, Cables and Installation Practice

A circuit protected by a 16 A MCB feeds a 2.5 sq mm copper conductor. Why must the conductor current rating be at least equal to the rating of the protective device?

  1. So that the voltage drop at the load stays under 2 per cent
  2. So that the protective device operates before the conductor is overloaded Correct answer.
  3. So that the conductor resistance remains below one ohm
  4. So that the earth loop impedance exceeds the device rating

Explanation

Coordination requires the protective device rating to be not greater than the cable current-carrying capacity, so overload current is cleared before the insulation is damaged. Voltage drop and earth loop impedance are separate design checks, not the reason for this rule.

Question 29Electrical Wiring, Cables and Installation Practice

Which test confirms that the insulation resistance between conductors and earth of a new 230 V installation is acceptable?

  1. An earth electrode resistance test using a fall-of-potential method
  2. An insulation resistance test with a 500 V DC insulation tester Correct answer.
  3. A continuity test with a low-reading ohmmeter
  4. A polarity test using a test lamp

Explanation

Insulation resistance is measured with a DC insulation tester, commonly at 500 V for 230 V circuits, and a reading of at least 1 megohm is generally required for a healthy new installation. The other tests check different properties of the circuit.

Question 30Electrical Wiring, Cables and Installation Practice

Why is the earth continuity conductor of a conduit wiring system bonded to the metal conduit at every box?

  1. To limit the voltage drop along the lighting circuit
  2. To improve the power factor of the connected load
  3. To reduce the current carried by the phase conductor
  4. To ensure a low-impedance fault path back to the source Correct answer.

Explanation

Bonding the conduit at each box keeps the metallic enclosure electrically continuous so that a fault to the enclosure produces a low-impedance path. The resulting fault current quickly operates the protective device and limits touch voltage.

Question 31Electrical Wiring, Cables and Installation Practice

A socket outlet circuit in a house is to be protected against residual current. Which device is intended for this purpose?

  1. An isolator switch with a 63 A rating
  2. A rewireable fuse of 20 A rating
  3. A residual current circuit breaker with 30 mA sensitivity Correct answer.
  4. A miniature circuit breaker with a 32 A rating

Explanation

A residual current circuit breaker with 30 mA sensitivity is used for personnel protection against earth leakage in socket circuits. An MCB or fuse responds to overload and short circuit but not to small leakage currents to earth.

Question 32Electrical Wiring, Cables and Installation Practice

What is the main reason for using a joint box rather than twisting and taping two conductors in a concealed conduit run?

  1. A proper joint box keeps the joint accessible and mechanically sound Correct answer.
  2. Twisted joints have lower resistance than any connector
  3. Taped joints are prohibited only in industrial buildings
  4. Joint boxes increase the current rating of the cable

Explanation

Joints must be made in accessible enclosures so they can be inspected and maintained, and a screw connector or thimble gives a mechanically and electrically sound joint. Twisted-and-taped joints loosen, overheat and cannot be inspected inside a conduit.

Question 33Electrical Wiring, Cables and Installation Practice

Which type of cable is most suitable for a wet, underground service connection where mechanical damage is possible?

  1. Ungalvanised steel conduit with bare conductors
  2. Single-core PVC-insulated wire in a conduit
  3. Armoured cable with PVC bedding and oversheath Correct answer.
  4. Flexible twin-twisted cord

Explanation

Armoured cable has a galvanised steel wire or tape armour that resists mechanical damage and, with a suitable oversheath, tolerates direct burial in wet ground. The other choices offer little or no mechanical protection for buried service.

Question 34Electrical Wiring, Cables and Installation Practice

A 230 V single-phase circuit draws 10 A over a 30 m run. Using a copper resistivity of 0.0175 ohm sq mm per metre and a 2.5 sq mm conductor, what is the approximate voltage drop in the phase conductor alone?

  1. About 2.1 V Correct answer.
  2. About 0.21 V
  3. About 4.2 V
  4. About 21 V

Explanation

Resistance equals resistivity times length divided by area, giving 0.0175 times 30 divided by 2.5, which is about 0.21 ohm. Multiplying by 10 A gives about 2.1 V in the phase conductor.

Question 35Electrical Wiring, Cables and Installation Practice

What is the purpose of a switch in the phase conductor rather than in the neutral conductor of a lighting circuit?

  1. It improves the earth continuity of the circuit
  2. It reduces the current drawn by the lamp
  3. It ensures the lamp holder is dead when the switch is off Correct answer.
  4. It allows the neutral to be shared between two circuits

Explanation

Placing the switch in the phase conductor means that, when it is open, the lamp and holder are isolated from the live supply. If the neutral were switched, the holder would remain at phase potential and could give a shock during lamp replacement.

Question 36Electrical Wiring, Cables and Installation Practice

Which material is used for the sheath of a cable that must remain flexible in cold outdoor conditions?

  1. Porcelain
  2. Rigid PVC compound
  3. Bakelite
  4. Polychloroprene rubber compound Correct answer.

Explanation

Polychloroprene rubber compounds retain flexibility at low temperature and resist weathering, so they suit outdoor flexible cables. Rigid PVC stiffens in cold, and bakelite and porcelain are rigid insulating materials, not cable sheaths.

Question 37Electrical Wiring, Cables and Installation Practice

What does the code IP44 marked on an industrial socket outlet indicate?

  1. Protection against solid objects over 1 mm and against splashing water Correct answer.
  2. Protection against dust and against temporary immersion
  3. Protection against water jets and against steam
  4. Protection against tools only, with no water protection

Explanation

In the IP code the first digit 4 means protection against solid objects larger than 1 mm, and the second digit 4 means protection against water splashing from any direction. Digits 5 and 6 denote dust protection and stronger water protection.

Question 38Electrical Wiring, Cables and Installation Practice

Why are cables derated when several loaded circuits are bunched together in one conduit?

  1. Grouping lowers the ambient temperature around the cables
  2. The conduit increases the supply voltage
  3. Bunched cables have higher insulation resistance
  4. Mutual heating reduces the heat each cable can dissipate Correct answer.

Explanation

When cables are grouped, each cable receives heat from its neighbours as well as its own, so the permissible current must be reduced to keep conductor temperature within the insulation limit. Grouping factors in cable-rating tables account for this effect.

Question 39Electrical Wiring, Cables and Installation Practice

Which accessory is used to control one lamp from two different positions, such as at the top and bottom of a staircase?

  1. A one-way switch
  2. A two-way switch Correct answer.
  3. A ceiling rose
  4. A push-button bell switch

Explanation

Two two-way switches connected by two traveler wires allow a lamp to be switched from either position. A one-way switch gives control from a single point only, and a ceiling rose is a termination accessory rather than a control.

Question 40Electrical Wiring, Cables and Installation Practice

What is the function of a fuse in a distribution board?

  1. To convert alternating current to direct current
  2. To open the circuit when current exceeds the rated value Correct answer.
  3. To limit the voltage supplied to the circuit
  4. To improve the earthing of the installation

Explanation

A fuse element melts when the current exceeds its rating for a sufficient time, thereby opening the circuit and protecting the cable from overload and short circuit. It does not regulate voltage, rectify current or affect earthing.

Question 41Electrical Wiring, Cables and Installation Practice

A three-phase motor circuit is being installed. Which practice is correct for the earthing conductor of the motor frame?

  1. Leave it disconnected because the frame is bolted to the floor
  2. Connect it to a separate earth electrode independent of the installation earth
  3. Bond it to the installation protective earth conductor Correct answer.
  4. Connect it to the neutral terminal of the motor

Explanation

The motor frame must be bonded to the installation protective earth conductor so that a fault to the frame is cleared by the protective device. A separate independent electrode creates a dangerous potential difference between earths.

Question 42Electrical Wiring, Cables and Installation Practice

Which test is performed to verify that the phase, neutral and earth are connected to the correct terminals of a socket outlet?

  1. Insulation resistance test
  2. Continuity test of the fuse element
  3. Earth electrode resistance test
  4. Polarity and earth connection test Correct answer.

Explanation

A polarity test, often done with a socket tester or a test lamp between phase and earth, confirms that phase, neutral and earth reach the correct socket terminals. Correct polarity protects users and ensures switches control the phase conductor.

Question 43Electrical Wiring, Cables and Installation Practice

A cable is to be run along a wall in a damp laundry room. Which installation method best suits this location?

  1. Cleat wiring directly on the damp plaster
  2. Bare conductors on porcelain insulators
  3. Flexible cord stapled to the wall
  4. PVC conduit wiring with sealed accessories and a residual current device Correct answer.

Explanation

Damp locations call for enclosed wiring, sealed accessories and residual current protection to limit the risk of shock. Exposed conductors and stapled flexible cord are unsafe in wet, humid conditions.

Question 44Electrical Wiring, Cables and Installation Practice

Why is a higher test voltage used for insulation resistance testing of a 415 V three-phase installation than for a 230 V single-phase installation?

  1. Three-phase circuits contain no neutral conductor
  2. Higher voltage circuits have lower insulation resistance by design
  3. The test instrument reads only at high voltages
  4. Higher-voltage installations need a test voltage above their operating voltage to reveal weak insulation Correct answer.

Explanation

The insulation test voltage is chosen to stress the insulation above its working voltage so that weak spots are revealed, so a 415 V system is tested at a higher DC voltage than a 230 V system. The required minimum insulation resistance remains a fixed value independent of system voltage.

Question 45Electrical Wiring, Cables and Installation Practice

What is the primary purpose of a conduit in a concealed wiring installation?

  1. To carry current in place of the conductor
  2. To act as the neutral return path
  3. To provide a protected route that allows conductors to be drawn in and replaced Correct answer.
  4. To increase the current rating of the enclosed conductors

Explanation

Conduit forms a mechanical route that protects the insulated conductors and allows them to be drawn in, rewired or replaced without disturbing the building fabric. Current is carried by the conductors, not by the conduit.

Question 46Electrical Wiring, Cables and Installation Practice

A distribution board has a 63 A main switch, a 30 mA RCCB and several 6 A MCBs for lighting. Which statement about discrimination between the RCCB and the MCBs is correct?

  1. The main switch provides the overload protection
  2. Both devices perform identical protective functions
  3. The RCCB protects against earth leakage while the MCBs protect against overload and short circuit Correct answer.
  4. The MCBs protect against earth leakage while the RCCB protects against overload

Explanation

The residual current device responds to imbalance caused by earth leakage, while the miniature circuit breakers respond to overcurrent from overload or short circuit. Each device covers a different fault type, so both are needed.

Question 47Electrical Wiring, Cables and Installation Practice

Which conductor size is commonly used for a domestic lighting sub-circuit with 5 A protection, and why?

  1. 6 sq mm, because lighting circuits need heavy cable
  2. 1.0 or 1.5 sq mm, because it comfortably carries the lighting load Correct answer.
  3. 10 sq mm, because voltage drop is always high
  4. 0.5 sq mm, because lighting loads are small

Explanation

Lighting sub-circuits on 5 A or 6 A protection are normally wired with 1.0 or 1.5 sq mm copper, which carries the small lighting load with acceptable voltage drop. Heavier cable is unnecessary and 0.5 sq mm is below the minimum permitted for fixed wiring.

Question 48Electrical Wiring, Cables and Installation Practice

What is the correct procedure before working on a circuit in a distribution board?

  1. Ask a colleague to watch the board while you work
  2. Open the main switch and begin work immediately
  3. Open the main switch, lock it off, prove dead with a tester and discharge stored energy Correct answer.
  4. Wear rubber gloves and work on the live circuit

Explanation

Safe isolation requires opening the isolating device, locking it off, proving the tester on a known live source and then proving the circuit dead, and discharging any stored energy. Working live or relying on a colleague is not an acceptable substitute for isolation.

Question 49Electrical Machines and Transformers

In a single-phase transformer, the component of the no-load current that supplies the iron losses in the core is called the:

  1. Magnetising current
  2. Core-loss current Correct answer.
  3. Secondary leakage current
  4. Load current

Explanation

The no-load current has two components: the magnetising component, which produces the working flux in quadrature with it, and the core-loss component, which is in phase with the applied voltage and supplies hysteresis and eddy-current losses. The core-loss component is therefore the one directly associated with iron losses.

Question 50Electrical Machines and Transformers

The induced emf in a transformer winding is given by E = 4.44 f N Φm. For a fixed applied voltage and frequency, if the number of primary turns is doubled, the maximum core flux Φm:

  1. Is doubled
  2. Is halved Correct answer.
  3. Becomes four times
  4. Remains unchanged

Explanation

Rearranging the emf equation gives Φm = E / (4.44 f N). With E and f held constant, the peak flux is inversely proportional to the turns, so doubling N halves the flux. This is why increasing primary turns reduces core flux and core loss.