Wall of Lightning

A crackling barrier of electricity appears at a point you choose within range. The wall appears in any orientation you choose: horizontally, vertically, or diagonally. It can be free floating, or it can rest on a solid surface. The wall can be up to 60 feet long, 10 feet high, and 5 feet thick. The wall blocks line of sight, but creatures and objects can pass through it.
When the wall appears, each creature in its area must make a Dexterity saving throw. On a failed save, a creature takes 4d8 lightning damage, and it is unable to take reactions until the start of its next turn. On a successful save, it takes half as much damage and can take reactions.
A creature that ends its turn in the wall’s area takes 4d8 lightning damage.

Any creatures wearing metal armor must make a Dexterity saving throw at the top of the round. On a failed save, the creature takes 3d8 lightning damage and is unable to take reactions until the start of it's next turn. 
Until the spell ends, you can use an action to cast Lightning Bolt at 3rd level, reducing the length of the wall by 10 feet. The bolt can originate from any point on the wall. If the wall’s length drops to 0 feet, the spell ends.

At higher levels

When you cast this spell using a spell slot of 7th level or higher, the damage increases by 1d8 and Lightning Bolt is cast at one level higher for each slot level above 6th.